Freelancer Chris Dahlen has gotten his hands on a near complete copy of the PC version of Braid, and has a lot of praise for it:

On one level - the one where I’ve made the least progress - you see a kind of branching effect. Say that you run from one end of the platform to the other, but as soon as you get there, you change your mind and rewind back to the start. After you rewind, you’re back at the beginning of the platform - but then a “ghost” version appears and retraces your last footsteps, while the present you can go off and do something else. Metaphorically, it’s like you’re watching two ways that your life could play out.

In fact, I guess it’s like Sliding Doors. The hard part is figuring out how to use this new ability to solve a series of jumping / lever / locked door puzzles, and how to picture yourself going in two separate directions at the same time - and that’s where this felt like calculus. Yes, I get the concept of calculating the slope at a specific point on a curve, but when I actually have to use it on a final exam problem, it makes a small spot on the left hemisphere of my brain go “groan.” That same flabby brain slice acts up when I play Braid.