I've played it for a bit and boy does it live to its source. They have most of the popular game mods already built in like DM (duel) TDM, CTF, Instagib and I think Rocket Arena. Game performance is very good and I haven't noticed issues. Auto matching works well. You can play in a browser window or full screen. There's access to the console to change some settings. I haven't tried usin my old config spec though. There are a lot of Team Arena maps in the rotation for those that like it.
The game has ads inside the maps and look like big signs or billboards placed in high trafficked areas. I didn't find them distracting at all.