Original Xbox Games

[Proverbial Jon]

Seriously, has no one even mentioned The Suffering? Good horror game if that's your bag.

But you can't go wrong with everything everyone else has said... except for Max Payne. I played it the other night and it's not a good port at all. Stick with the PC for Max Payne.

 

[Wayneguard]

Unreal Championship 2 was great in its day and its worth the insanely low price now even w/o the online componenet. Thief: Deadly Shadows is great. Tenchu: Return from Darkness is also great. It's basically tenchu: wrath of heaven with 2 extra (and awesome levels).

 

[bawkbawkboo1]

All of the ones I was going to say have already been posted, with the exception of Dreamfall: The Longest Journey, which is at least worth a rent.

EDIT: I just remembered that Dreamfall is 360-compatible, and it also has a PC version I think

One of the few Xbox1 games I have that is NOT 360-compat. is Prince of Persia: Warrior Within. However, that is on all the other platforms.

 

[Troublesome Lagomorph]

most of the worth while games like KotOR, are backwards compatible.

Yeah, this. I can't thing of any good ones that are still not backwards compatible.
Or on pc.

 

[Nutcase]

"Psychonauts" and "Ninja Gaiden: Black" are essential to that ugly chunk of fun that is the XBOX.

No point in playing, much less buying, XBox version of Psychonauts when you can get the PC version for $10 at GOG and play it in glorious 1920x1200 or whatever your display resolution is.
Ninja Gaiden Black is available for download on the 360. That said, from what I can google it sounds like it has no difference to getting the XBox version (which you can also run on the 360).

 

[-Samurai-]

I'd have to say Conker: Live & Reloaded. The redone multiplayer was crap, but the remake of the original singleplayer was great.

I don't know about that. I loved all aspects of Conker: Live and Reloaded. Personally I thought the multiplayer was ok. Way too hard to figure out certain things but overall it was playable. Single Player was hysterical though.

I preferred the N64 multiplayer over the Xbox one. I just didn't like how they over-complicated it. And they didn't have my favorite map for TDM.

 

[Plurralbles]

Ninja Gaiden
Mercenaries
KOTOR
Fable
That's a decent grouping.