Trying a playthrough in hard. It shows that the game was built with timestop in mind, and now that it's limited it's way harder to do things, but still possible.
Gets even worse when you can get up to three timestops at a time but the checkpoint "refills" it to two, even if you have three! I don't know what controls the timestops regenerating either.
Things are frustrating enough that chopping up heads suddenly feels tempting.
The wall and the final boss will sure feel like hell once I get to them.
EDIT: Oh man I found something funny
I fought the wall and somehow killed it just as those two pillars were falling. The pillars remained intact even after the "YOU DEFEATED" screen, and refused to die if I attacked it. I pressed R wondering if it could do anything, and the game crashed.
EDIT2: Yeah the final boss is insanely difficult. You remember that long bridge right before the final screen? You need one timestop to get through it unless you have insane stamina or spent several tries figuring out how to go with enough of said stamina (double jump first without running to get enough distance, then start running and jump just as the 'steps' get too steep to run over, you should get through that way). You're left with one or two, and you need those to counter her timestops, because to even dodge you need an insane time window that's not even worth it.
Still, it was difficult in the 'trial and error till you find an anticlimatically easy way to win' kind of difficulty. Just hug the wall on either side to force her teleporting to come from only one way. And never try to fight her directly, just block her knives from a distance and wait for your timestop counter to recharge, then when she teleports in activate it and fight her from there on. The circle of knives is the worst of all, since you can do nothing about it at all. Even if you timestop and hit them all, they're all still solid and you can't roll out of it, so it's either a wasted timestop or part of your health gone for no damage whatsoever to the boss unless she's close enough.
Had to try that boss several times before easily beating her with just one potion used and no powerups upon finding that method. Not the fun type of difficulty. Decapitating her felt good after that, though. This was all with a pure damage build, no points spent on HP, stamina, or timestop duration.
EDIT3: Trying that NG+ feature on hard. Enemies get far, far stronger. Wall on the new area instakills you on default health with a missile. Final boss can drop you from full health with that mid-health attack. Exponential increase on exp needed to level up means you're pretty much fucked. Afraid to think what NG++ on hard would be.
