All time favorites:
1. Operation Flashpoint
2. Operation Flashpoint - Red Hammer
3. Operation Flashpoint - Resistance
-----6 Years of non-repetitive gamplay and over 10,000 user-made professional quality addons (tanks, guns, enormous islands, etc) kept the game alive and new every single day over the internet.
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Currently playing:
1. Armed Assault (Has gotten better since 1.12, but still not perfect.
2. Battlefield 2: Project Reality (Mod) - Like the teamwork
3. Crysis (May be done playing it if reality mods aren't released soon) - Like MESA only, the smaller maps are too chaotic and CS/UT like for my taste.