I liked Reflex Arena the most out of the post-Quake Live arena FPS'. It's a huge pity that it didn't really take off. I feel like they made a terrible mistake hedging their bets with catering to the CPM community. From what I saw it alienated the VQL players by using CPM mechanics, and the CPM players shunned it in the end because it wasn't an exact clone of CPM. This was a poor decision, in my opinion. One that ended up dooming what could have been an amazing game.
I was in the closed beta - it really satisfies the quake style deathmatching itch I've had lately.