I spent some time with the Joint Ops demo last night, so here's my initial impressions. Keep in mind that this demo is actually the early Beta that they have been testing for some months now. I'm assuming that the final game will have improvements.
Pros:
Huge levels, with nice looking foliage (for this game type, anyway)
Weight-based inventory. Weigh yourself down with lots of ammo, or just carry a couple of magazines.
Ammo dumps and weapon stockpiles at key locations.
Allows you to change out weapons in-game, rather than waiting for a respawn.
Good selection of voice commands. (I liked how it had a function that would "ask" for passengers in vehicles)
Fairly lethal damage for firearms
Good hit-detection
Cons:
A little on the "arcadey" side
Weapon selection is small, especially compared to Soldner
No voice-comm support
Somewhat laggy (although my friends PC was running like C-R-A-P last night, so that may have affected it)
Players seemed to retain their previous uniforms when they switched sides (ie, a "rebel" had a "joint ops" uniform)
Teamwork can be hard to come by (a fault of online gaming in general, no the game itself)
Small arms sound FX were pretty weak. Easily fixed, but I'd prefer it to sound good out-of-the-box
All in all, I think it has potential. But I'm still going to wait and try Soldner before I plunk down my $60 CDN on one of these games.