Maybe you'll like Survarium (when it comes out).
It's a "survival" MMO FPS game that's sort of a spiritual successor to the STALKER series, but with a different setting (although still similar). Instead of being about the Zone and the fallout after the Chernobyl accident it's about a natural disaster that ultimately makes the environment hazardous and unpredictable (they kept the anomalies thing though, that's a direct nod to STALKER). There's a number of devs video updates on the game's development progress on YouTube and I believe they're nearing the closed-beta phase (last time I checked anyway).
And, well other than that one... with online features or specifically only for online play? That's a tough one to be honest, at least as far as being outside of science fiction is concerned. If you like WWII to modern settings then have you tried Medal of Honor? If not of course I would have suggested Call of Duty (the older ones up to CoD4 I guess) but you've played them. And sure Day of Defeat is good (the Source one that is, the older one was fun back then I loved it myself but it hasn't aged well in my opinion), I guess you could still keep it in mind for those occasional rainy week-end days when you're bored out of yourself.
The last FPS game I bought was Hard Reset and I love it, but it's very old-school style. That is at least game-play mechanics and levels design wise (for instance with rotating power-ups around, and small level secrets by blowing up walls, etc). It feels very much like DOOM or Quake with modern graphics, but I don't think that one would be your cup of tea.