For those of us unfamiliar, can you be more specific about what has changed from the core ruleset?
Damn, that's a lot of stuff. Some examples include even the enemies, they have very different HP numbers, AC numbers, CR (challenge rating) and abilities. Then there's the weird stuff with advantages/disadvantages based on height, how "backstabbing" works, and spells are sometimes quite different too, and the class implementation is far from faithful, aswell as many actions that are bonus actions instead of full actions, and lots of actions like Dodge, Ready and Disengage missing. Then there's how reactions are implemented, aswell as how some abilities and actions should be able to be applied upon a hit, and so on and so forth. Honestly, the list goes on but these are certainly some of the main points.