That mod was awesome. They somehow managed to make slow motion powerups work in a multiplayer action game without forcing it on every player in the map!
Also had a strange RPG community entirely separate from the main game… funny how these random subcultures evolve in unexpected places.
Another HL mod I remember fondly in similar veins is "The Specialists". If I remember correctly, it came out around the same time as The Matrix, and had all the fun moves like running on walls in slowmo, jumping forward/sideways and shooting in slowmo, and lots of other stuff. I think I recall it being possible to play both in 1st and 3rd person too, something that was kind of new at that point, unless I misremember.
I think at that I point I probably spent as much time with The Specialists as with Counter-Strike itself (and a cracked copy of 3DS Max 8 for making my own models of course).