I recently started playing Urban Terror after seeing it posted here. The gunplay, weapon design, and map design all remind me a lot of CS as well (I never played Quake 3 so I have no reference point there).
The developer of action quake 2, Gooseman, went on to create CS as a mod for half-life.
Urban terror is the Q3 port of action quake 2.
AQ2 still has a small community of players. I get on occasionally for the nostalgia hit. I’ve never found an FPS that’s as fast paced and difficult to master (movement primarily).