You probably got the "First Day" lite version of HalfLife (ATI card, right - Rage, probably).

It takes awhile to "get into" the game - stay with it at least till "hell breaks loose".

There are also lots of "expansion" packs for HL including Blue-Shift & Opposing Forces (where you get to play as a guard or soldier) - some of them (Blue Shift, I think) even "update" the HL graphics engine a bit.
Definitely RtCW if you liked MOHAA. Unreal if you like Half-Life.
And MDK2 if you like wicked humor.
And you're STILL in the bargain bin.
I am on Thief II right now (close to halfway). Very different as it is a "sneaker", not a "shooter". I like it! Finally NOLF (No One Lives Forever) and NOLF II are pure gaming "fun" where you get to play as a Ms "James Bond 007" (type) Superspy.