I personally love the remastered idea where the game is actually modified. I feel like that is a great way to spice up an old game, as long as you do it right. For example, in the Sonic franchise, new levels and playable characters were added to some of the classic titles, and they were done in a way that was: 1) respectful, and 2) fun.

I would LOVE:

1) DO change the Halo 2 campaign. Not fully to where it's a new game, but I really couldn't play through the (IMO) mediocre campaign more than once. The STORY aspect was fun, but the GAMEPLAY was annoying to me. I could tell it wasn't finished. Something about the physics or AI or something -- I don't know, I really hated it. I am not on the bandwagon of "Don't touch the campaign, for it is pure and classic." Change. It.

2) Leave multiplayer alone, update graphics. Multiplayer is where the game was best, so no reason to change that I feel.