Could be a good game, but I can see a few problems with playing a game with that many players. Frontlines: fuels of war (or something similar) on the 360 has/had a large player count - around 100 on some servers, IIRC, but I always felt like a single player game, mainly because nobody used to speak to each other, or work in a team for that matter.
So this game needs to have a decent squad system which encourages people to actually talk to each other (do they give away mikes as standard with the PS3?), and work in a team, if it's really going to be any good.
Although I suppose the fact they are able to make a game on this scale playable without lag hopefully means that other games will benefit in the future.
I played the BETA of this a couple of days ago (Available for download from PSN), its not too bad. a bit arrsey trying to get used to the control system if your used to the Call of Duty Series. I never noticed any lag of connection problems (except downloading the 2GB Update after the initial 32MB server download).