I'll give you a run down of what to expect out of each title, so you can figure what you wanna play based on your own preference.
Resistance - Arcadey shooter. You jump, shoot lots of cool sci-fi guns. There's online dedicated servers up for up to 40 people at once. There's offline co-op of up to 2 people and offline deathmatch of up to 4 people.
Ninja Gaiden - Hack and slash game. It's really very fun and extremely challenging. The gameplay mechanics are top notch.
Godfather - It's like a Grand theft auto style game. The story line isn't too bad actually and you get to go around and take of businesses and make them pay you protection money. Lots of fun and definetly a good fix until GTA4 comes out if you like rampaging.
Motorstorm - Arcadey racing game. Probably the best looking game on PS3 right now. Downside is no splitscreen... but it's great, and there's online versus. It's just a lot to fun to play, and I'm not a huge racing fan.
Virtua Fighter - This is my favorite fighting series. There are no fireballs you shoot out of your hands or supernatural shit. All the characters do real fighting moves and the game is balanced and done to perfection unlike any other franchises.
Enchanted Arms- it's only $20 at gamestop. It's an old school style, turn based RPG.
Oblivian - Kind of a hack and slash rpg... sorta. It's a little like playing a MMORPG offline. highly customizable characters. Big world, lots of quests. My biggest complaint is all the mobs are relative level to you. I get enjoyment out of leveling up in RPGs to just own everything I see. Doesn't really work here.
MLB the Show - A really realistic baseball sim. A must buy if you like baseball.
Rainbow 6 - Tactical shooter. It's like Socom. There's offline coop. Online coop of up to 4 people. Lots of different online versus modes, like team deathmatch. You need a headset to play this online because it's very tactical.
Fight Night Round 3 is a good game to buy if you like boxing.
Darkness is good if you like shooters. It's the third best I'd say behind Rainbow and Resistance, get those first.
Armored Core's a decent mech fighting game, but the customization system is needed to play and kinda complicated as all shit.