Remember people, Halo was released back in 2001. Everything, except the leveldesign, was very well executed (No endboss, great open battles, incredible A.I, graphics, jada jada jada). Halo 2 wasn't as good as Halo 1 though.
As a sidenote, i never got into HL back in 1998. The graphics were meh, the soundtrack was awful, the story a pop-corn action-flick, the gameplay was on rails (but solid nevertheless), and horrible end-boss and end-levels.
I liked Unreal 1 much more.