I'm gonna chime in and say that the op expresses much of how I feel as well. Action economy sounds good, degrees of success, tiered proficiency, all very neat and with great potential. I also like the potential for customization, but mostly feel underwhelemed by the options presented.
I also feel like the content doesn't let the system shine as much as it could. For example, the fighter and other martials needs more feats that allow for playing with the action economy in interesting ways. More feats that either tack riders onto an action, or more maneuver like feats that only cost one action so that you can combine them in more diverse combinations. I want the three action economy to be as flexible as possible,and the feats as written don't let it be that way. And the martial types need more class feats that are useful regardless of weapon/armor/equipment used, but that's just a content concern.