Even for a shooter fan, you should really try out the games you plan on getting before you get your ps3 - they might not be what you expect.
I bought R2 and was extremely disappointed. I was excited about the 60+ player matches but it just wasn't my thing - I do love 60+ players on PC games when there's huge maps and vehicles involved, but R2 doesn't have any of that. It should've made up for that with some awesome gunplay but even that part of the game feels weak - the guns have either have small amounts of recoil or literally none at all, they feel like paperweight and don't really giving you a sense of actually shooting or firing a weapon, and the game's auto-aim is pretty strong. The campaign is about as generic as it gets - typical case of aliens assaulting earth, you're the guy everyone's counting on. The bosses are huge and impressive, but sometimes feel more like tech demos because of the actual fights being pretty simple and repetitive. Strongest point in the game is probably the 8 player co-op.
Killzone 2 is definitely a great game. It was one of the huge reasons I bought my ps3, but even I was slightly dissapointed in some areas, mainly with the lack of variety and options. Even though online matches support 32 players, it gets ridiculously messy and chaotic - this game definitely feels much funner with less people. You could end up liking this game alot - I personally know much more people that would take KZ2 over R2.....I sure as hell would anyday. Though this game does lack weapons, the ones they do have are great, all the way from the "feel" to the sound - very satisfying to shoot.
Not sure if you're into 3rd person shooters but I recently bought Warhawk a week ago (after having the demo installed for ages - gave me many hours of good fun) and it's definitely one of my fav shooters now. It wasn't even on my list of games to get before I bought my ps3, it completely surprised me. One of the things I like is that it's somewhat similar to many PC shooters (to be specific, the Battlefield series) - it involves heavy use of vehicles on large maps. The game supports 32 players, but they should've added more considering how huge the maps are. I'd say this game has more tactical elements than R2/KZ2, thanks to the simple rock-paper-scissors style that the vehicles use - there's not really a single weapon/vehicle that can murder everything, so often you'll rely on your teammates for stuff like having a tank take out anti-aircraft guns so your team can get some air support. Of course, the game isn't perfect. Like KZ2, it's abit of a pain tryin to play with friends. On a random note, it also has 4player online splitscreen which is huge for me. Again, like any other game, try it first - it might not be your thing.
If you're buying a PS3 hoping to get some good shooter action, you actually might wanna save your money.
