You're right, it had genuinely good level design and great gameplay modes out of the box, something you can't say about Quake since Quake2.
I used to load up Rocket Arena, fire up some mp3s, and just trickjump my way around the maps for ages. That game got the FEELING and PHYSICS so perfect that, for me, it didn't even particularly
need the combat at times. Just the movement was fun on its own*. I can't wait for Quake Live to go public, wish I'd managed to get into the beta. I still play Q3A occasionaly, although it suffers from that thing where all the guys on it now have been playing it almost non-stop for a decade, and they can hammer the living crap out of you.
* Thankfully, the likes of Nintendo seem to be cottoning onto this these days - control is where most of the innovation SHOULD be, fuck the graphics whores who've always been over-pampered anyway. I remember watching a games documentary in the mid-90's where the guy who made Ecco The Dolphin talked brilliantly about the
controls in games, and how great it was when it reached the point where you could do complicated things while barely even thinking about them.