Unreal, Quake 2, Jedi Knight, System Shock 2, SiN, Blood 2, Hexen 2, Rainbow Six, Turok 1 & 2. There were a number of great FPS games available at the time.
I did enjoy most of those games, but wouldn’t use them as examples of equivalents of Half-Life. Some did some things better than Half-Life but others were worse in every category and were superseded (e.g. Unreal.) Great list of memories!