I’d guess the textures have been redone at a higher resolution, though it may simply be that things look awfully sharp on something that isn’t a PSX on a CRT TV. The backgrounds are pretty blurry at any sort of high-resolution as they’re all pre-rendered images, but the character models are surprisingly gorgeous. Graphically, it’s actually held up rather well. It “feels” pretty much identical to the original, rather than being a crappy alternate version of it. I repeat: I don’t have much of a problem with this.
I will note that battles feel like they’re running slower than 30, but I think that’s just the combat animations bits and pieces like the UI and the damage numbers are all silky smooth compared to the slightly choppy combat animations. Every bit of gameplay is running at 30, while all cutscenes are at 15, and considering the cutscenes tend to make use of pre-rendered animations that’s hardly a surprise. In terms of framerate, Final Fantasy IX runs at a mix of 30FPS and 15FPS, but I’m 90% sure that’s exactly the same as the PSX original so I’m not really going to complain. As represented here by a little dolly that a grown man with a pink beard should not be able to immediately pull out.
