Operation Flashpoint is by far the most realistic (and IMHO, enjoyable) shooter/war game there is. I think the graphics are fine, though OFP2 should be REALY impressive. The best thing about OFP is the mission editor, you can set up an endless variety of missions and real world combat situtions, from invasions, to occupations and ambushes. Since it is basically 1 shot one kill (on both sides) it really helps to give you the feel and fear of a shoot-out.
The IA, typically the most trying point of any vieo game, is very well done. Your teammates are not useless fodder, but actually fight, and fight well. The enemy can be cunning and deadly to an oblivious panicky fool (can adjust their sill level in the mission editor).
The weapons are very well done, and you can dl a endless varition of them. However, some of the weapons seem a bit under or over powered (MP5 1 shot kills at 300 yards, AR15 kills at 400+ yards). OFP2 is rumored to include jamming and weapon malfs which increase or decrease depending on field and enviormental conditons! I believe the US military actually uses an upgraded version of OFP for combat simulation? Never the less, it's a great game and deserves a try by any shooting fan.
Edit** BTW, I GOTTA DL that UN patch!