Recently picked up the old game Operation Flashpoint. I skipped it the 1st time around after feeling overwhelmed by the demo. Now that I've cut my teeth on other tactical games like Ghost Recon and Raven Shield, I've really been enjoying it.
I picked it up on Ebay for $2 for the GOTY version. I've been trying different mods by checking out the posts on the Operation Flashpoint forums.
So far I've mainly tried total conversions such as FFUR, EECP (above pic),Y2K3, FDFMod and CSLA. I'm amazed by the amount of mods (unit replacement, gameplay enhancements, missions/campaigns, etc.) that are available. I should have picked this up long ago but at least I know have tons of gaming to look forward to. An updated version, Armed Assault is also due out in a couple months so I'll be checking that out as well as good tactical SP/MP games are hard to find nowadays.
Besides the forums, other good OFP sites are:
OFP Mission Database
Operation Flashpoint Editing Center