Sonic Adventure

The Good
This was Sega's attempt at a "killer app" for the Dreamcast, a platformer game starring the titular character on an adventure with his friends, who are also playable characters. It features state-of-the-art (for the time) graphics, as well as a catchy soundtrack produced exclusively for the game and stunningly good sound effects.

Not to be overlooked is the game's game-within-a-game, the "A-Life" artificial intelligence system that functions as the brains behind the baby "Chao" creatures found in one room of the main hotel in the beginning of the game, as well as select locations throughout the rest of the game. These "Chao" creatures can be raised by Sonic and the other characters, and provide an interesting sub-game when used in combination with the Dreamcast's Virtual Memory Unit.

The Bad
Characters not named 'Sonic' could've been explored more in-depth. In addition, Tails' missions are a bit of a letdown; they mostly revolve around racing Sonic throughout a given level, which can get boring at times. Big's missions are usually no more than glorified fishing simulations, and E-102's are just confusing most of the time.

The Bottom Line
If you've got a Dreamcast or have access to someone else's, this game is a must play, even in 2009. The storyline, graphics, and sound are simply amazing, and were well ahead of their time. I'd go so far as to say it's one of my favorite console games of all time.