info gotten from EJraven at ACO
Here are some of the CONFIRMED new features of NEXUS:

1- Weapon's parameters changed to balance unbalanced parts.
2 - Fromsoftware turns development to Mr. Pot & AC2AA development team staff for mission disk.
3 - Parameter of some Core (heads, arms, cores and legs) parts changed.
4 - Parameter or stats translated into Japanese (All Japanese games have its game stats and part's stats in English)
5 - A.I. Arena deleted.
6 - Double lock deleted and new, faster lock system formulated.
7 - Sight standardization: WS (Wide lock) has been shorten and ND has been enlarged
8 - Weapons color customization for all weapons possible. (You can color all of your weapons now!)
9 - Frame tuning option (I don't know what this Japanese Magazine means with this? I will find out soon)
10 - Seperate right hand weapon and left hand weapon sights
11- EO Core optimized: Improved accuracy, reload time and AP/Def points strengthening.
12 - New Cores (More on this new cores once I see the intro video this weekend!)
13 - Head and back radar new changes:
a) Head radar will only display the enemy and its effective radar range, some parts SKYEYE will also display incoming missiles (Same as AC3 and AC3SL)
b) Back mounted radars will display objects, walls and obstacles in detail of every map or arena, enhanced radar capabilities.
14 - Hard landing will be implemented again as well as a change in the braking when coming out of an OB rush. The change in the weight/speed formula will allow AC to move faster and to have higher speed and velocity.
15 - Enviromental interaction.
16 - New element, or new part (secret element announced! I will find out what it is don't worry guys!)
17 - Uncertain how many parts have already been deleted (rumors has it that solid shields are gone and that a new type of hybrid solid/energy shield has been formulated)
18 - Adjustment and correction of heat formula, OB core heat emition changed.
19 - Weapon breaking abolished! (WB is gone forever!)
20 - Generator recovery speed equation changed, faster reload time.
21- Blade behavior changed, range enlarged (Blades no longer go over opponents and increased accuaracy on side cutting, blade power upped and air blading correction for more accuracy.

Info from ac garage
Contents
-0- Gameplay
-0.1- General Gameplay Changes
-0.2- Controls
-1- Features
-1.1- Part Tuning
-1.2- Weapon Colour Customisation
-1.3- Part Changes/Deletions
-2- Parts
-2.1- Head
-2.2- Core
-2.3- Arms
-2.4- Legs
-2.5- Booster
-2.6- FCS
-2.7- Generator
-2.8- Radiator
-2.9- Inside
-2.10- Extension
-2.11- Back Weapons
-2.12- Arm Weapon R
-2.13- Arm Weapon L
-3- Single Player and vs Maps
-3.1- Single Player
-3.2- Vs Maps



-0-Gameplay

-0.1-General Gameplay Changes

Heat will become much more important in ACNX. We will still have the 'output down', but now when heat reaches 80% an alarm will sound (danger heat?), now while the heat goes down, your GENERATORS output goes down considerably. When your heat goes down this seems to be called 'Thermal Runaway'. I beleive 'Output Down' may be a little different in the way that it is activated and remedied. (Heat levels mainly). More on this when I get it. 'Dancing' (Holding L1 and tapping R1 or the opposite) will now be much harder to do as pressing L1 and R1 at the same time will make your AC come to a complete stop.
-0.2-Controls

Take note that the controls ARE re-mappable Strafe Left & Right: Move Left Stick Left & Right
Walk/Run forwards & Backwards: Move Left Stick Up & Down
Look Left & Right: Move Right Thumbstick Left & Right
Look Up & Down: Move Right Tumbstick Up & Down
Point of view reset: 0
Boost jump: L2
Boost movement: L2 + left stick
Fire Left Arm Weapon: L1
Fire Right Arm & Shoulder Weapon: R1
Change Weapon: R2
Extension ON/OFF: L3
Inside use: X
OB EO ON/OFF: R3
Drop Right Arm & Shoulder Weapon: �� + R1
Drop Left Arm Weapon: �� + L1
Drop Extension Extension: �� + L3

-1-Features

-1.1-Part Tuning
Parts such as the Head, Arms, Core, Legs, Boosters Generator and Radiator can be tuned. There is limits to how much the part can be tuned and it also costs money. There may be more tunable parts and I will update this as I find out about them. (E.G. Radiator, Boosters, FCS).

-1.2-Weapon Colour Customisation
Your ACs weapons can now be coloured.
This is not with the standard RGB system though (the way your AC is coloured), you have to choose from several colours.
There are 5 colours to choose from, which means I am missing one. (It could be brown).
Confirmed Colours:
Red
Orange
Yellow
Green
http://www.gpara.com/comingsoon/0130acnexus/img/img20040130-11_04a.jpg

-1.3-Part Changes/Deletions
Some parts are being deleted, these are 'clone' and unpopular weapons. Also the stats of parts are being changed, an example of this is the generators, which are supposed to charge faster. EO's will now be able to hit moving targets from mid range, apparently the Energy EO could even be mistaken for an energy CANNON. The EO cartridge will also move more smoothly and not be "feverish" MWG-MG/800 will be changed. The CWGG-GR-12 seems to now have 15 grenades and has 2400 attack power. http://rsrecord.s26.xrea.com/acn/g2.jpg The GNL-15 has 12 shots and 3050 attack power. This might not be correct. The BZ-50 now has 40 ammo, but still has 1400 attack power.

-2-Parts

Total number of CONFIRMED Parts: 101 (Around two thirds of the total AC1 parts)
-2.1-Head

CHD-01-ATE
CHD-02-TIE
CHD-06-OVE
CHD-07-VEN
CHD-SKYEYE
CHD-MISTEYE
MHD-MX/RACHIS
MHD-MM/003
MHD-RE/005
MHD-MM/007
MHD-RE/008
MHD-SS/CRUST
MHD-MX/BEE
MHD-MS/VANGUARD NEW!
HD-VI-099 NEW!

-2.2-Core
CCL-01-NER
CCL-02-E1
CCM-00-STO
MCL-SS/ORCA
MCM-MI/008
MCM-MX/002
MCH-MX/GRP

-2.3-Arms
CAL-44-EAS
CAL-66-MACH
CAM-10-XB
CAM-11-SOL
CAM-14-DUSK
CAH-22-NIX
CAH-23-XB1
MAL-RE/HADRO
MAM-SS/ALS
MAH-SX/VI NEW!
MAW-DSL/FIN
CAW-DC-03
CAW-DMM80-1 NEW!

-2.4-Legs

CLM-01-EDF
CLH-XV-MSGR
CLH-STIFF
CLF-D2-ROG
CLC-05-ACE
CLR-03-SEOLF
MLL-MX/077
MLL-SX/0094 NEW!
MLM-MM/ORDER
MLM-XA4/MOX NEW!
MLH-SS/RS
MLB-SS/FLUID
MLF-RE/005
MLR-MX/LEAF

-2.5-Booster
CBT-FLEET
MBT-NI/MARE
CBT-01-UN8

-2.6-FCS

-2.7-Generator
CGP-ROV6
CGP-ROV10
CGP-ROZ
KGP-ZXV1

-2.8-Radiator

-2.9-Inside

-2.10-Extension
CWEM-R20
CWEM-R10
CWEM-AS40
MWEM-R/24
CWEM-R20
MWEO-R/32 NEW!
KEBT-TB-UNS

-2.11-Back Weapons
CWM-S40-1
MWM-S42/6
CWM-S60-10
MWM-S60/12
MWM-MM16/1
MWM-MDM2/1
CWR-S50
CWC-CNG-300
CWC-GNL-15 CHANGED!
MM-AD/20
CRU-A10
MWX-MX/STRING
CWM-MM100-1 NEW!
MWC-RAG/30 Rail gun NEW!

-2.12-Arm Weapon R
MWG-RF/220
CWG-RF-160
CWG-ARF-120
CWG-SRF-80
CWG-MG-300
MWG-MG/350
CWG-MG-500
MWG-MG/FINGER
CWG-HG-80
CWG-BZ-50 CHANGED!
CWGG-GR-12 CHANGED!
MWGG-XCG/20
CWG-LRF-CHROME NEW!
MWG-LRF-VIX NEW!
CWG-BRF-270 NEW!

-2.13-Arm Weapon L
MLB-LS/003
CLB-LS-2551
MLB-MOONLIGHT
CLB-LS-3771
MLB-DUALGUN NEW!
KES-ES/MIRROR
MWG-GSL/72
CWG-MGL-150
KWG-HZL50

Remember that AC3 was meant to have inside missile launchers, so there is always a chance a part or 2 wont show up in the game.

-3-Single Player and vs Maps
see the page with new parts also
-3.1-Single Player
Guard Freight Train AC1

-3.1-Vs Maps
Night City AC1
Desert Arena ?? New or PP/MoA??
Iceland ?? New or PP/MoA??

info from a member of ACO (written while playing Nexus)
Revolution: The "old" game, with thirteen episodes, which are remakes of missions from the PS one games, a music player(31 tracks), a poster gallery(11), illustration gallery(60) a movie gallery (the little movies that accompany each episode - 15) and a Series movie gallery (8). I assume the last are the movies from the previous games.

The first thing I noticed was the new controller setup. I like it, a lot. Forward, back, and strafing movement are controlled by the left stick, turning, look up, look down by the right. Weapon switching, left arm, right arm, and boosting are all controlled by the shoulder buttons. It took a little getting used too, but it works really well. For one thing, I'd always had trouble using R and L weapons simaltanously in the old setup, but here it's pretty easy. Square resets your screen, X is Inside, Triangle + the appropriate button drops that piece, O seems to control EO and Overboost.

Music is decent, and the graphics have gotten a little polish.

VS:
Network and I link
So, looks like you have to be at least in the general vicinity of the people you want to play if you want to go multiplayer.

Military District
Underground Works
Limestone Cave
Crest Base
Structure
Ruin
Snowy Field
Abandoned Factory
Arena

All of the above are like their SL versions.

Dune
Decreased visibility, a couple of hills. Medium area.

Marine Base
Ankle deep water, heavy fog, a couple of islands and a highway. Large map.

Training Space
An arena with a couple of small ledges.

Born City
City with scattered buildings and a high ceiling. Reminds me a lot of a smaller version of the City map from MoA.

Floating Arena
Platforms linked by walkways in space. Small map, with an upper, middle, and lower area.

Missions:
Referred to as 'episodes,' with two or three missions comprising each one. For example, in Episode 2, the first mission is defend the sub, then attack Chrome base

Evolution: The new game.

The missions have been interesting so far. You certainly make a lot more money this time around. Four missions in and there are already contracts out for more than 100K. Nothing really exceptional yet. The most annoying thing is, if there's an arena, I can't find it. There's an 'Arena ranking' list, which ranks you according to points acquired on missions, and I've gone on a couple of missions that were arena style fights, right down to the replay option, but no independant arena.

Among other things, this has made weapon testing harder. The two solid thing I've pinned down are that deeks have been toned down (when two missiles are fired at once, one will go for me, the other goes for the deek) and the whole 'magazine' concept in action is rather interesting.
They'll fire for a second or two, then there's about a half second pause to reload.

You also get continous heat increase from boosters and overboosting will shoot you right into 'error' although you don't loose armor from boost heat. It does however wreak havoc on your generator. The design I've been using, while the heat gauge is in the read, the energy gauge is dropping on its own. The way heat affects a match is definitely going to be different now.

I haven't done much blading, but the Halbred is simply huge. All blades have the ability to make a beam attack, although it is much weaker than the OP-I version.

My immediate evaluation is, well, it's more AC. That's certainly not a bad thing. I think that I have to say I like the Japanese names for weapons. I've got the Pixie 3 / Fairy MG combo going on the Selena Core. (MG 800 / LMG 229 / GRP). Fear the power of Fae!