The only decent 'fps' style MMOG at moment is Global Agenda which has pretty enjoyable PvP but it's not as large scale as Planetside was. IMHO planetside was the best MMOFPS especially when they'd introduce a free month once in a while. Because then, everyone that enjoys the game but didn't want to pay-to-play would hop on board and we'd have massive 3 way battles with hundreds of people that would last for hours.
One of my fondest MMO memories was during a free month of Planetside during a battle that spanned half an island between all three factions and on my side a big group of folks formed a tank rush in the big suits (it has been so long I forget what they are called, we were on purple team and at the time they had the best ones) and some 60 people coordinated in these tank suits and rushed a base in waves. It was so damn fun.
So yea, do Planetside Next right SOE and give players a lot to play with before you charge them for anything. That was really the failing of the first game. Pay-to-play for a game that was good, but not as good as Tribes or other free-to-play games of it's time.