LOL, that's why I haven't bought any since CoD4 and World at War either. I got THOSE on a big Steam sale, too, so I didn't pay much. I've not bought any CoDs since, haven't bought MoH since Airborne, and haven't bought a BF game since BF Vietnam!!
Other than staying current on my Arma2 stuff, I think the only series I've bought all of have been the Clancy Splinter Cell, GR, and R6 games. That said, GRAW2, R6 Vegas 2, and Conviction were probably my least favorite of each series. However, I have most of them in Steam so I can go back and replay Raven Shield or Chaos Theory or GR+expansions at any time. I often find replaying the old ones more enjoyable than the new ones.
I played OFP:DR, but this Black Friday RR was only $12 and I thought that too high. I paid $5 for DR and that was about what it was worth, so I'll get RR when it drops to $5.
Now in non-military FPS, there are some great ones out there. Deus Ex HR (called an RPG, but it's so FPS-like I think of it like one as opposed to the Mass Effect/KOTOR-style RPGs I usually play) is great. Serious Sam 3: BFE is great.
The Jedi Master