Granted, some of the level design in X8 was a bit odd. Just being experimental, largely. Not all of those experiments produced good results, but none of those stages are really "annoying" in the way some stages from previous games were.
Indeed, some of the items are way too expensive. But then there's that glitch, so no problem.
Although flying Zero is a much more fun glitch to abuse.
You also get awesome music
and voice acting that doesn't suck (for the most part, anyway)!
Though, the one thing that's unique to X8 that I really liked and doesn't get enough appreciation is the way the tag team system works. Characters can recover some damage when not in use. If your character dies, the other one comes in to take their place and, and the dead character can recover. And then there's the double attack.
Point being, the whole is very much greater than the sum of its parts. You know, as a
team should be. That was hands down the game's best innovation.
X7... yeah, it had potential, but it was poorly implemented. They only give you the ability to move the camera in full 3D areas and an awful lot of the camera angles they give you in the semi-3D sections really don't work very well. Prime example: the second part of the Palace Road stage would be a hell of a lot easier
if you could see where the [tornado fang] you're going. But instead, you're running towards the screen.
(as an aside, why isn't there a checkpoint before the boss fight in that stage?)
The other major annoyance was those attacks which knock you down. Recoil from strong attacks is one thing, that's to be expected. Being made to fall on your ass and lose total control of the character for several seconds so you have no chance to take advantage of your temporary invulnerability is another entirely. Especially when you consider how often that excessive recoil knocks you onto spikes and into pits.
The rescuable reploids feature had the same problem it did in X6 where if you let one die, they're gone, although in one way it's worse and in another it's better. It's worse in the sense that they die a hell of a lot more easily. It's better in the sense that even once they're dead, they're not
completely gone forever because they'll be back in New Game+.
And on that note, that's another thing I really don't like: not being able to fully power everyone up in a single playthrough.
Still, that's an improvement over X5, X6, and Soul Eraser where fully powering up both characters on a single file is impossible no matter what. Which, besides being irksome (yeah, I'm a completionist, so sue me), breeds a tendency to just use one character, give them everything, and kick the other to the curb. I'd probably use Zero a lot more in X5 and X6 if giving him powerups didn't mean not giving them to X.