So many great games, so little time. Kinda depends on what you're looking for:
Quantity: Oblivion, specifically the PC version. There's already a ton to do in the main game/expansions, but when you add mods it becomes a truly massive and fully customizable experience. Plus, the game's still got an active modding community 6 years after its release, if that tells you anything.
Quality: Portal. Hilarious dialogue, witty puzzles, awesome ending, and none of the recycling old puzzles or forced love story cliches that plague so many otherwise great games. Might be short, but it enters, does what it intends to do absolutely flawlessly, and leaves before it's overstayed its welcome.
Story: Bioshock. Easy to understand, yet it has a mind-bending plot twist that will guarantee you'll never look at a particular phrase the same way again.
Multiplayer: Rock Band 2 with friends in-person, or Call of Duty 4 for online.
Quantity: Oblivion, specifically the PC version. There's already a ton to do in the main game/expansions, but when you add mods it becomes a truly massive and fully customizable experience. Plus, the game's still got an active modding community 6 years after its release, if that tells you anything.
Quality: Portal. Hilarious dialogue, witty puzzles, awesome ending, and none of the recycling old puzzles or forced love story cliches that plague so many otherwise great games. Might be short, but it enters, does what it intends to do absolutely flawlessly, and leaves before it's overstayed its welcome.
Story: Bioshock. Easy to understand, yet it has a mind-bending plot twist that will guarantee you'll never look at a particular phrase the same way again.
Multiplayer: Rock Band 2 with friends in-person, or Call of Duty 4 for online.