This is distinctly a guide for fogeys. Do not use this to judge what the favorite child in your life would like. These games are for boring, thirty-or-forty-or-fiftysomething you.
Guitar Hero, Legends of Rock (Wii) I have my eye on the World Tour bundle, which apparently opens up the possibility of drums and singing. But this is the staple that has kept an untold number of bloggers mesmerized for hours. The idea is simple: there are five buttons, which correspond to notes on the screen; your job is to hit the notes in time with the display, and the song. But the game is almost too fun; I actually developed tendonitis in my index finger at one point, trying to master a song. This is what it looks like if you get really, really good:
But don't worry; if you're over twenty-five, you will never get that good. There's a beginner level that uses fewer keys and goes a lot slower. I recommend investing in a second guitar, because your friends/spouses/children will definitely want to play. Or you could also get the World Tour bundle, which comes with one.
Mario Kart (Wii) I was actually too old/female for original Nintendo, so I'm fresh to this, but it's embarassingly fun. You drive around in circles. You fall off things. Your three year old nephew beats you, repeatedly. It's like the distilled spirit of Christmas.
The game comes with one Wii wheel, but I recommend getting at least one more for multiplayer; we have four.
Dance Dance Revolution (Wii) The most aerobic game available for Nintendo. It sure beats staring forward on an elliptical trainer for forty minutes.
Okami (Wii) Weirdly beautiful, weirdly entertaining game from Japan. It's hard to describe--"Myst with a Paintbrush" isn't a bad stab at it from a hooked friend.
Civilization IV (PC, Mac) Years after it came out, I'm still playing. It's simply the best world-builder out there. War, science, religion . . . I'm not sure it's ever come up to Civ 2 for me, but it's still light-years ahead of any other competition.
Railroad Tycoon III (PC, Mac) This is the other game that I go back to year after year. I'm a rail buff, so of course, I would love this game, but even people who don't care about trains find it deeply satisfying to build a working company, and see towns grow up around your railroad.