These were already said, but I'd like to emphesize I think these are the main balance problems:
1) Being able to deal too much damage at once: Speed potions/Haste's extra action in 5e is one extra attack, here it's an extra 'attack action' that translates to 3 attacks for a fighter, or exta spell on caster. Quicken-spell and multiple smites on the same turn are also to blame for excessive burst damage. The existence of many strong weapons (that add an extra damage die or more per attack) makes this even worse as your hasted fighter gets that extra die 6 times per turn.
2) Shove distance / push with thunder arrow distance etc. are all yeeting targets really far into instant death chasms. In many circumstances these chasms don't even need to be there and are just pretty-scenery.
and in other planes with 'free eternal featherfall' I don't think these chasms should kill, rather the ones thrown to them should find their way back to the fight
3) enemies getting bonus action throw-paralyzing-poison attack on top of their 2-attack action. Paralyzing a character is powerful and scary enough, no need for them to also attack on the turn. There's a huge contrast between some creatures spending all their turn just to dash and get conveniently closer for you to kill them, and other creatures just doing one nasty thing after the other....
