Maybe I'm not hardcore enough to appreciate all the extra peripherals and such, but Halo and I'm supposing Halo 2 was made with the S - Type in mind. The turn rate limit is an example of that.
I'm also a little wary because when you factor in that there will likely be a slight aim assist included in Halo 2, just as their was in Halo. Since controllers are not as precise as mice it just makes sense.
In another point, I think this has the potential to start a lot of arguements on XBL. An example might be MechAssault, an old and tired title I know. But the glitch in the game based on the use of a 3rd party controller to get nearly unlimited jump jet usage and extra speed.
Imagine if you will, a few weeks from now you're in a game and you find yourself just destroyed by your opponent, every shot a head shot. Never catching someone with their back turned. I can already hear shouting matches and accusations flying about whether or not the mouse adapter is 'fair play'.
I've been part of these arguements before when it came to fighters and sticks (back when I was ignorant and all). Some ascribe to the idea that 'If it's there, use it' while others I suppose myself to an extent feel that some things just offer an unfair advantage, or at least unbalance the game.
At least the PC port of Halo took out that aim assist feature since mouse use was of course assumed. But I would expect Halo 2 would have some sort of aim assist to it. Couple that with a mouse, and I'd say you have a recipe for domination, and a lot of hot headed fights.
I'm on my way now to dig myself a trench. Because I get the feeling this post won't be well received by many, and perhaps get me into hot water.