I never got into Halo, didn't find it particularly "fun"
Which is strange since I like FPS games.
Halo is floaty with projectiles, military FPS's are grounded and heavy with instant bullets.
Kind of like comparing a kart racer and a car racer. Fans of one fork of the genre certainly don't have to like the other.
DEUS EX!
It restored my hope in gaming and nicotine gum.
HR? I haven't played it, but I do have it on Steam. Of course the original DX was awesome, but that was in an era with System Shock 2, CS Beta, Half Life, Quake 2, Jedi Knight, etc. not exactly a dry spell in terms of quality