My favorite is easily the original Halo.
Especially now that I just recently got a tube TV. I've been using flatscreens for a few years now, and the original Halo just isn't balanced for them; comparatively speaking, it feels sluggish, looks wonky, and sounds awful on them. On a tube, it's crisp, it looks good, and its audio balance sounds a hundred times better (no exaggeration there at all; flatscreen speakers cause music-sfx clashing in HCE in places where, on a tube, the sounds flow together perfectly).
Half-Life 2 would possibly be a runner up if I had to nominate something.
Especially now that I just recently got a tube TV. I've been using flatscreens for a few years now, and the original Halo just isn't balanced for them; comparatively speaking, it feels sluggish, looks wonky, and sounds awful on them. On a tube, it's crisp, it looks good, and its audio balance sounds a hundred times better (no exaggeration there at all; flatscreen speakers cause music-sfx clashing in HCE in places where, on a tube, the sounds flow together perfectly).
Half-Life 2 would possibly be a runner up if I had to nominate something.