Uno delivers a perfect online version of the classic card game.
Gameplay: It's Uno, plain and simple. The rules of the game are cut and dried (match the color or number of the pile, forced to follow action cards, etc), but it does allow for some customization. It's a ridiculously easy game to learn if you've never played, but has enough strategic maneuvering to keep even the most experienced player looking for a new challenge. As far as the actual game goes, it doesn't get any more accurate than this.
Visuals: It's hard to knock Uno here either. There is really no need for much flash in this game. If you really need variety, there are a couple different decks available for download over Xbox Live. The cards look just fine and everything is easy to see.
Sound: Here is where Uno trips just a little bit. While the sound effects are acceptable, the background music is a bit repetitive and cheesy. It would have benefitted from the ability to add your own music to a custom soundtrack. The music won't drive you nuts, but it might annoy you just a little bit.
Value: It costs less than a real Uno deck, is occasionally available for free, and has online multiplayer and various game types. This game is an excellent value whether you pay full price for it or not.
If you're looking for a social Xbox Live experience, Uno is an excellent place to look. It's almost perfect...only a corny soundtrack keeps it from being a flawless virtual experience. All board and card games should be converted this well. If you're a fan of the card game, you should definitely download Uno.