Scorched Earth

Get tank. Point Gun. Shoot. Watch Explosion. Do happy dance. Simple, right?
I've generally found that it's the simple games that will suck your soul out through your eyeballs. This is one of them. The kind of game that looks like a quick fix to play while your significant other is getting ready for your date, only to discover that when you take a break, she left 4 hours ago by herself. The kind that will keep you pasted to the computer for really no apparent reason.

The trick is to play with friends, and alcohol to keep yourself from becoming a recluse.
I first encountered this game in college. A group of friends of mine and I would play Doom II over LAN (yes, I'm showing my age a little here). We'd also play Warlords II (a great TBS game if you can get it). This game showed up one day, and we got sucked in.
This game will actually bring you closer together with your friends. Since you all play on one screen, you'll sit closer in order to see what the others are doing. This game, by its very nature, also leads to a lot of trash-talking which, at least in the circles I run in, brings the group closer. Names of tanks lead to running jokes. Running jokes leads to tank names.
This is the game that used to be a big party in the dorm lounge. We'd drag someone's tower in there and just blow each other up to the sound of clicking glasses and shouting and laughing college students. I can't wait to play this with my son (who's only 3 right now). I hope it will generate a closeness between the two of us as it did with my friends those many years ago.
OK, here's the lowdown:
Sound: Nothing special, but nothing annoying
Graphics: Again, nothing special. The explosions are pretty neat, but otherwise fairly Spartan.
These would seem to be bad things, but I think they actually help. The game is amazing in its simplicity. If they tried to make it fancier, it would take away the charm, make it more difficult to have that party atmosphere, and generally detract from what is "The Mother of All Games".
Gameplay: Again, simple, easy to pick up, but has some subtleties that will show the differences between a novice player and an experienced one. What's the old saying? "5 minutes to learn, a lifetime to master".
Replayability: 3 words.... Never Gets Old