The classic card game makes a great game after fragging people all day
This game really is all about friends. This is a very social game, since it doesn't require much attention, you will find yourself talking to people about things other than the game. You will meet friends, or play against friends, and have lots of fun talking, laughing, and playing a barely competitive game of Uno. This really is the best game to play with friends. It is also very relaxing, so after a long day of flanking, fragging, and getting headshots, it's nice to sit down with some friends and play some Uno.
There are a couple downfalls to the game. It is repetitive, obviously, since it's Uno and can't be much else. Also, if you are playing with someone that gets really competitive, it isn't relaxing anymore, especially since the competitive person is screaming in your ear how he "owned you". In my experience, someone even went on to make fun of my GamerTag...
However, as long as you play with your friends, the latter problem will be fixed. Now, the achievements are pretty easy, so expect an easy 200 GamerScore as well. However, since this really is a fun game, you can't be called a GamerScore junkie or anything. Plus, it's the best game in the Xbox Live Arcade with the cheap price of 400 Microsoft Points, which the equivalent of $5!
With a cheap price, a relaxing mood, and the fact that it's Uno, this is a game you CANNOT pass up. You will lose a lot more than you will win, but you will find that you could care less.