DIPRIP wasn't very fun. I downloaded it and played it for about 30 minutes before giving up on it. The controls felt like they took 1-3 seconds before what I input had any effect, which kind of ruined it for me. Maybe it would be better if I were playing it with my Xbox controller as thats better for driving games.
Insurgency is fun, but the lack of information displayed on the HUD is kind of annoying. Great game though, just wish they would fix that issue.
Syngery I had a tough time finding any decent servers to play on, and it kept giving me errors about not having HL2 and Ep1-2 installed when I have all 3 of them. I'm not sure if thats a problem with the game or the server but that was a hindrance to my enjoyment of it.
Zombie Panic: Source is good. A lot of the maps are a little to campy for my taste though.
Haven't played or heard much about Age of Chivalry, but it seems pretty similar to PV&K II, which I wasn't a big fan of as source doesn't work well with hand to hand combat.
As for other mods, I'd recommend The Hidden: Source. 1 vs 8 teamwork based game to hunt down a genetically modified awesome killing creature.