Monks, in my experience, are better tanks naturally. I recently played a game with 2 monks, my barb, and a DH. Both the monks were my friends and had recently hit 60. In act2 with gear massively inferior to mine, they could take hits better than me and regen wayyy better. My buddy who has been in inferno as long as I have, was disgusted that they were doing so well. We hit a wall around the time you need to get Krulle's head in Act2 because their dps really started to hurt (we could not down packs before enrage)
Why they do so well is quite easy to understand. Monk's regen is easy compared to a Barbs. Their heals are controllable and reliable, and their LoH combined with immunity is money. They can get resists cheaper and on fewer pieces of equipment (OwE) so it gives them more freedom to get other stats. Their main stat adding to dodge naturally is also a huge factor.
In comparison Barbs have to count on revenge for a heal, which is a chance to proc skill that has a small range and only grants life in comparison to mobs you hit. It is also one of the stronger attacks in the Barb's tree, so it makes sense the life regen is not OP. Dreadnaught is my other health regen skill, which doubles as a movement or escape spell, but again it is dependant on hitting enemies. The largest issue comes to LoH, where a Barb can do fine tanking until he needs to stop hitting due to frost bombs, AS, or a big swing from a mob where the monk can just pop Serenity and giggle, or seven sided strike to become immune to damage will still regening. Finally Dex is a better defensive stat than Str.
Now take the arguement the other way and I would like to see a monk out dps my barb. Not gonna happen.
That's my rant on melee. I don't think a monk is better than a barb, I just think they are more efficent tanks. Nothing is OP, and I love my barb just fine. Just my observations.