I really like the barbarian's Danger Sense. If it weren't likely unbalancing, I'd suggest making it an Initiative bonus too.

The fighter's Combat Expertise replacement ability might have power issues, as a mid-level fighter could use it to gain an insanely high AC. Also, one of the main benefits of Combat Expertise is that it leads to many useful feats. I would suggest that the fighter can use this feat for prerequisites unless that contradicts other considerations of yours.

Unarmed attacks, by the PHB, already Power Attack at a 1:1 ratio. They're a specific exception to the rule about light weapons. Maybe the monk could instead treat an unarmed strike as a two-handed weapon under certain circumstances?

These are neat overall. I like the fact that they're focused on detail much of the time. I never could figure out why rogues didn't get Knowledge (dungeoneering) as a class skill.