I don't own an XBox, so obviously I can't try it out, but Im assuming it runs halfdecently well, otherwise I'd say it's just an all around crappy game.
Framerate
never exceeds 30FPS and it rarely gets that high. Calling it crappy kind of leaves out the gameplay portion which most people due tend to find more important then the graphics engine
The Halo rendering engine sucks IMO, although it is what many people seem to think they want. It is a shader loaded game that stops relying on textures and starts putting that more advanced hardware to use.
In that aspect Halo is hands down the best engine to hit the PC to date. The game runs much better then TRAoD(and looks better too).
Not to mention, if I spent $60+ on a game that my XBox couldn't run acceptably, I wouldn't feel to good abou it.
Only paid $50 for mine. The performance isn't that far out of the norm. It runs better then GTA3 on the PS2, the most popular game in the last couple of years across all platforms. When you are using a controller, you don't miss the framerate nearly as much as you do on the PC with mouse and keyboard. Don't get me wrong, one of Metroid Prime's big advantages over Halo was that it ran considerably faster and significantly smoother(talking GC MP vs XB Halo), that said the game still kicked @ss slow or not. It would have been better with better framerates, one of the big reasons I picked it up for the PC.
Is it slower on the XBox than a high end PC?
Hell yes, a
LOT slower.
In that case I'd say there isn't a single platform out there that can play it at acceptable speeds unless you drop detail levels enough to make Quake III look better.
Leave everything cranked in terms of features and drop your resolution down to 640x480. You should be seeing well over 100FPS+ as the norm(over 300% faster then the XBox). Does Quake3 look better? In terms of the traditional sense probably yes, it runs very fast and due to the speed you can crank the resolution and AF/AA and play at very crisp settings. None of the graphics cards have close to enough power to do that in Halo, the shaders are simply too demanding.
This is the future that a lot of people think they want for PC gaming. When you hear all the hype about shaders, Halo is the best example to date of what current level shaders can do on the PC. Half-Life2 uses shaders as an accesory to an engine that looks incredible without them, so the game ends up looking significantly better then a game that looks like crap without any shaders(anyone can try it for themselves in Halo, it looks real bad withou shaders). DooM3 is Carmack, and I can't fault anyone for not being up to his level in terms of building a graphics engine(noone is, apologies to Tim if he reads this

). That said, Carmack took DX7 level features and did as much as he could with them(obviously the end result is stunning).
Bungie obviously could have done better with Halo's engine had they been given more time, but the limitations of the XBox are part of the reason why there isn't a good 'fallback' when you disable shaders(which would have made most people happy with the PC port). They couldn't use a bunch of high res textures, not when they only have 64MB of total memory to work with.
Anyway, when you hear all the hype about pixel shader heavy games think Halo. When HL2 hits people will see the game still looks incredible without them, and D3 is using GeForce1 style features allowing for much better performance, Halo is the best example, performance and visual wise, of a shader heavy title. IMO, it is worth dealing with the very low res and playing through the game @640x480, really one of the best shooters to hit in years(if not the best). Have to play it on either Heroic or Legendary to enjoy(otherwise it is way too easy), but certainly a killer game.