The modded version of ArmA 1 i have running is brilliant. The AI search and clear open buildings. SpecOps will sneak up on tanks and lay satchels indepenantly of any mission editing. Just put random troops anywhere on the map with gaurd or the modded 'dismissed' waypoints and you have a dynamic warzone.
The other mods i found include better evironment visuals, forecasted weather, accurate balistic, accurate AI spotting/pathfinding/recognition distances, accurate penetration at range, windage and elevation MOA setting, range cards, more realistic flight modeling, realistic tracer mod, realistic bleeding and wounding, the possibilty to make enemy platoons surrender and lie face down if they are being thrashed. ..the list just goes on. Then there are the hundreds of user created weapons/units/objects/maps which make hours of mission editing fun.
How could anyone not like this game? Its basic in so many areas, that's the beauty for me, rather than these super fast action shooters on the consoles. I will upload a recent MD500 support mission i made to you tube if anyone wants to see how damn good ArmA 1 looks when you set it up right.