This is probably the best of the trilogy, with some awesome setpieces and the best story Halo has done.

I've probably beaten this one like 15 times, and I have yet to get sick of it. This especially whips in co-op, where you and a couple of friends can just go nuts on these massive battlefields.

The multiplayer is also iconic, essentially being the blueprint for the rest of FPS multiplayer gameplay. Forge, Griffball, Snipers, just a cavalcade of nostalgic memories of late night gaming.

If you are only going to try one game in the series, 3 or Reach are my suggestions.