After playing with two of these in my Sefina deck, Time Warp is one of my favourite cards in the game! Not because it's particularly super powerful (I think it's good, but not exceptional). It's just that it feels so fun to play.
The first time I played this card after buying it, I did an action that caused the Act deck to flip, and then I failed a resulting test which directly dealt me a permanent trauma. Not only did Time Warp undo that trauma, the fact that it fully reverted the Act back to the previous Act felt SO powerful, being able to manipulate such an important game aspect. (Note, however, that I think being able to timewarp the Act or Agenda is probably pretty rare, since those don't often flip due to an investigator action.)
It was also really funny to me that after traveling back in time to undo that action and unflip the Act, I just immediately went back in and did it again. If I had got the trauma on the second attempt... at that point I would have deserved it. I just needed to succeed at that check though, and I did the second time!
Especially in multiplayer, playing this on another player's action to help them fix the mess they caused from their action is just delightful. "Oh something went wrong? No it didn't." Especially if other players aren't expecting it, and they get all their commited cards back in hand, unexhaust assets they used, etc. Just remember you can't use it after a player is defeated on their action, because then Time Warp can no longer target them.
Sometimes it can be hard to remember all of those details of what changed during a complex action, which in my opinion is part of what makes this card fun, but I can see it as a reason not to play Time Warp. It can be a bit of a headache. I definitely recommend reading through the FAQ here about undoing effects such as shuffling a deck. Sometimes you simply can't play Time Warp if you can't get the game state exactly back to how it was, but in many cases it's fine. "A randomized deck is a randomized deck." It doesn't necessarily have to go back into the exact same unknown order.
Also note, however, that Time Warp can sometimes let you know at least what the top card of a deck is. I once played Time Warp after taking a simple draw action where I drew my weakness. I went back in time, putting the weakness back on top of my deck, and then if I didn't have a way to shuffle my deck, I simply would have drawn the weakness at the end of the round. Thankfully, I had a Quantum Flux ready to go.
Having Time Warp in hand feels good too, even before you play it. It's like a defensive trump card, similar to Ward of Protection, but for player actions instead of treachery draws. It feels like a backup in hand similar to a Lucky, though Time Warp is more situational.
