After 4-6 hours a day for four days, Apache has finished Halo. The verdict? In his words, best visuals, best gameplay, best presentation.
Before Halo, my pick for the game that presented itself the best would be Half-Life. With all the nice scripted events, the small talk with the security guards and scientists, and just how Valve laid the game out (that is, until the end, where things got goofy) made Half-life an exceptional game. Bungie really one-upped Valve with Halo though, and once you play Halo, chances are you'll think the same.
The fly in the ointment, if there is one? The controller. Apache freely admits he sucks at gamepads and would much, much, much rather play it with a kb/mouse but says that didn't stop him from enjoying the game at all.