Just tried it, and these are my preliminary opinions:
Gameplay feels kinda slow compared to BF2, using the sprint is slower, vehicles feel a lot slower and sometimes even aiming is very sluggish too; it's weird how most real life military hardware seems to get faster as time passes, but the designers took the decision to make the vehicles slower for this version supposed to be set in the future. The infantry weapons looks weird, almost everyone carries huge guns and firing them don't feel as satisfying as using the BF2 weapons was.
Graphics are good IMHO. Dunno why, but the graphic style of this game reminds me of Tribes 2. Special effects like EMP charges and the improved lighting look awesome! Runs great maxed out at 1280x960 on my system (except for FSAA, which I disabled), but artillery makes the FPS dip a little bit, great explosions btw!
I just don't like how all foot soldiers look almost the same no matter which class they are.
The hovertanks are great, (I use tanks most of the time in BF2, so this was my first vehicle choice
), and take a lot of damage, counter-meassures are very effective against AT rounds, but the driver don't get to use a turret mounted machine gun which helped a lot against infantry in BF2, I feel kinda open waiting for a guy to plant a C4 charge on my tank while waiting to neutralize and capture the flags though so far it hasn't happend yet
Anyway, the cannon is very powerful, it just takes a bit to aim effectively against infantry, but once I got the hang of it I was racking up my kills in no time
The sound is ok, though I miss the real sounds from the previous version, lots of weird futuristic sounds coming from all directions while on a gunfight
So far, BF2142 feels more like a total BF2 conversion than like a new game IMHO, but it has great potential, I can't wait to try the other maps.