The graphics are pretty dam good, considering that you can go anywhere you want (unlike CoD games, which are still just corridors like the origional doom etc.). The AI isn't perfect, but it gets the job done. Where the game really shines is the editor and the fact that the AI is dynamic.
Screw the campain, you can get into the editor and have a nice village assult etc. up and going in a few minutes. Because the AI is dynamic, no matter what you do, where you put enemies etc, it will always work well (at least, always work at the same level of AI, which can sometimes be annoying).
if your looking for an action FPS, don't get ARMA2. its a good game, but its not that type of game. Its a "oh, imagine if xx attacked yy in zz way: i'll go make that right now and then play it" kind of game.