In fact, the only real flaw with any of these games is that some of them just weren't very good to begin with. The first two X games are just about on par with some of the better games in the original Mega Man series, but the measure of quality declines bit by bit the later you get into the series, until you get to X5 and X6, which just aren't very good at all (though X5's bosses are all named after members of Guns N' Roses, so that's pretty awesome). Mega Man Anniversary Collection had the same problem; games like Mega Man 6 for the NES and Mega Man 8 for the 32-bit systems weren't exactly barn burners in their day. But here, there's less of the good stuff to make up for the lack of quality inherent to a few of these games.
More in the way of extra content would have made Mega Man X Collection a much more appealing product--though it's still pretty good as it stands.
There are also fewer extras to partake of. There is a fairly extensive art gallery you can paw through as you unlock content for it, and there's one unlockable bonus game in the form of Mega Man Battle and Chase. Battle and Chase is a polygonal kart racer for the PlayStation that never saw the light of day in North America, and after playing it a few times, it's not exactly tough to see why. The game is surprisingly fun for a concept as goofy as a Mega Man kart racer, but it doesn't have a lot of lasting value. So essentially, you don't get any of the producer interviews, anime episodes, or other crazy stuff found on the original Anniversary Collection. It's unfortunate, because it would have been cool to get some more background info on the franchise through one unlockable medium or another; but sadly, there are no such bonuses. On the plus side, at least there are no wild differences in unlockable content between the two versions of the game. The PlayStation 2 and GameCube versions of the game both have the exact same content across the board, so you're not missing anything by picking one over the other.
Mega Man X Collection isn't nearly the resounding success that Capcom's first Mega Man compilation was, but it's far from a failure. Any fan of the Mega Man X series that doesn't already own all these games in some form or another ought to give this collection a try; it does a fine job of chronicling the series' ups and downs, and provides a good measure of extra content to back it up. Certainly, the package would have benefited from more in the way of unlockable content--especially since there are really only two truly great games on this comp, and the rest merely range from solid to mediocre. But as it is, X Collection will please the series' longtime fans, and serves as a good primer for those who never had the opportunity to check out these games back in the day.