I think I've read somewhere that the idea that the monk was overpowered basically came from the idea that they had the largest list of class abilities listed on their table.

And yes, in a trap-studded dungeon with a DM who isn't well-versed in the rules, the monk can appear powerful at first. I mean, he get's 2d10 damage! The fighter's longsword only has 1d8! Even if it's a +5 longsword, that's still only 9.5 average damage, compared to the monk's 11! And yes, I must admit that I actually thought 2d10 damage was a huge lot when I first saw the monk.