If you're after a shooty game for Christmas, why not check out Armed Assault? It's got a blend of closed-quarters battle as well as large-scale military conflict, so whichever one you like, you'll be happy. Upon loading, you're dunked into the middle of an expansive and engaging storyline, fighting against enemies both smart and aggressive, continually filling the massive landscape with challenges.

...and if you really want it, you can grab the demo now.

The demo version only covers a small part of the game - with a map covering the southern part of Sahrani (without the more expansive northern part), three multiplayer modes (as opposed to 16+ and singleplayer), basic weapons and vehicles (a mere portion of the full 30 different models of each). There is also no editor included in the demo - but the full game has a mission wizard, mission editor, built in scripting language and full support for user-made addons and mods.

Of course, you could always just go play outside or something - but where's the fun in that?