If you like RPGs then Oblivion is your game. I would also strongly reccomend Dead Rising. It's an incredible RPG light. A ton of action and a lot of fun. But here are some games I would reccomend in order of preference.
1. Elder Scrolls IV (Oblivion)
2. Dead Rising
3. Mass Effect
4. Stranglehold (great shooter)
5. Crackdown
6. GTA IV
Mass Effect is an incredible Action RPG. You get to choose whether you want to be good or evil. Theres powers and guns.. the works.
Stranglehold is a crazy shooter game where you look like a complete badass japanese dude who has the ability to use "Tequilla time." basically you do slow motion stunts. Its surprisingly fun. watching a video review wont do it justice. check it out.
crackdown is a free roaming rpg light. way too much fun. unfortunately a little repetitive at times, but honestly worth a buy. you're a super charged cop with super strength, speed, and an arsenal of weapons and vehicles at your disposal. you can also jump like over buildings and stuff. amazing game.
GTA IV is a little over rated in my book, but a solid buy. I'm playing it right now. It's definitely addicting after a while and worth a buy once you've checked out the other games I've mentioned. I wouldnt reccomend the others if I didnt believe they were worth that 60 bucks.
sorry about the novel. trust me. i know my games. i know ull fall in love with those games. btw... oblivion is the most fun of all of them, but it does start out really slow. its a heavy duty rpg. takes some time to get into it. but definitely worth the effort. ive logged about 200 hours over the past 3 years. incredible game.