My first impression of the Monk is that it doesn't look customizable enough. Really the only thing that makes it special, the thing that differentiates it from a Fighter in play, is the Monastic Traditions. I like that there's a good mix of the more mundane martial arts as well as elemental attacks, but the fact that you make one choice at character creation which determines ALL of your special powers for the rest of your career just grates at me. Choose Path of the Phoenix, you're the Fire Guy. You won't be throwing around Stunning Strike or healing yourself with Wholeness of Body. You're just...pigeonholed.
The per day limits on ki are also a bit annoying. It's these abilities that will make you "feel" like a Monk in combat, and you just don't get to throw them around often enough. Spellcasters get cantrips now that make them feel like spellcasters, why can't Monks get something like that? There's nothing here that conveys the feeling of that crazy guy without weapons fluidly darting around the battlefield hitting large numbers of foes.
Granted, he IS unarmed. But the martial arts playstyle is just fluff. His fists count as a d6 light, finesse, bludgeoning weapon, but he basically just walks up to guys and hits them, kinda like a Fighter. Except that even this incarnation of the Fighter gets his Expertise dice, which being an encounter resource will get a lot of "screen time." Meanwhile the Monk, with his daily ki limit, is going to be encouraged to "save" his big powers and playing that resource management metagame doesn't seem even remotely appropriate for a martial artist. He should be showy and fight in a distinctive way. Right now he's just "walk up to a guy and hit them until one of you dies" the vast majority of the time.
About the only thing this version of the Monk gets right (at least out of the gate) is Mindful Defense, which is the same basic mechanic that the Barbarian gets to make up for the fact that he's not wearing armor. Predictably, the Monk gets to add his Dex and Wis mod to AC.
A swing and a miss on this one.