1.Oblivion: The best RPG to date. It has a great leveling, skill and attribute distribution system and tons of armor and weapons. You can explore a gigantic living world full of monsters, bandits ect. with amazing graphics. The story line is fairly good and has good replay value.
2.Mass Effect: This "Star Wars" like RPG probably has the best storyline of any xbox 360 available. It is a addicting adventure full of unexpected turns and twists. The leveling and armor system is average and gameplay is fun. The three different classes are all unique and interesting. The freedom to explore uninhabited plants is exhilarating.
3.Call of Duty 4: This shooter has good graphics and great multiplayer. The unique customize weapons is extremely cool but, the campaign is short. Good sound effects and music. Lack of co-op online multiplayer on same xbox is disappointing. Still a must have for xbox 360.
4.Burnout Paradise: Mixes racing with free world exploration. Lots of different events where you can choose your route to the destination. Crashing system is spectacular and stunts tricks are sweet. Over 85 cars and motorcyles to choose from. Great multiplayer to play with friends and hundreds of challenges. No flaws in this game. Only reason it was #4 was that I like RPG more than racing.
5.Halo 3: Probably the best online multiplayer available. With co-op story mode and thousands of people online this game is the greatest when it comes to coopertive and competitive play. The forge and theatre features are neat. Minor glitches. Overall fun shooter.