Although to be fair, performance on oXbox isn't exactly rock-solid either. Halo 1 has always been a spiky game, and coop exacerbates it. Halo 2 dials back drastically on the dynamic stuff, though, and is substantially more stable.

: I remember playing the campaigns on the MCC to get the cutscenes, and it was
: strange because even with the old graphics, it just felt wrong. I
: initially chalked it up to the games just not aging well, and games with
: more weight to the enemies and character control being superior.

: But playing the original versions, I felt no such lack. They were perfect. It
: wasn't the frame rate, because I prefer 60fps universally. The Naughty Dog
: games that get PS4 versions (Uncharted, Last of Us) are all way better in
: 60fps. That's not it.

: What could be different? The only thing that's different besides frame rate
: is the code base (Halo PC and Halo 2 Vista as a base), widescreen
: rendering, and a new controller. Are there other differences?

Those things might have a hand in it.

XB1 controller's sticks feel like they have a different response curve, and who knows how the controls were mapped across the ports.

The animations and such were authored for 30fps, and might be different from Uncharted/TLoU in that there's a snappier, choppier core style with Halo.

As for widescreen rendering, I know that the modern ports have a history of compressing the vertical FoV for split-screen modes, at least in Halo 1, instead of just expanding the horizontal FoV. For MCC they patched this to be less extreme, although IIRC it's still not quite like the original (I can't test it because I currently only have 1 XB1 controller).

Then you just plain have the visual and audio differences. The former probably doesn't impact the core control feel that much (the biggest thing I can think of with Halo 1 is that the pistol's two impact sprites shoot off together in the port instead of one after another), although the latter is filled with style and timing differences (such as the pistol having a sharper bang in the port versus a rolling cadence in the original, or the sound for switching to the AR).