My good friend loves monks and he played mostly monks back in HS. It was ok, cause we played role play heavy, combat light games. And rest of us in group had penchant for picking classes with interesting fluff more than picking classes that are "good".
But, in combat heavy games, with people who did optimize their characters for combat efficiency ( not even full charop, just decent optimization), monks fall flat. They need good Str for dmg, Dex for AC (they can't wear armors), con for hp, wis for DC. For someone who needs to get up front and personal with enemys, he has rather low AC and HP and not much damage. Conceptually, monks were highly mobile hit and run fighters, but that didn't really translate into the game cause how action system work. You can't move, attack, move. And if you move more than 5 feet, you cant use full round action.