The ones in the first collection were obviously much easier and less time consuming to obtain than the ones in the second collection. The "secret image" and "secret track" ones were annoying because they had more criteria than stated (which included completing all the X Challenges, which thankfully allow you to play on easy mode because normal mode might as well be hard mode). X1's were a piece of cake. X2 had the tricky Magna Centipede one where you had to avoid all the spotlights, but still nothing too difficult. I had to play X3 twice because I'm used to killing Bit, Byte, and Vile by finishing them off with their weaknesses, so I had to face Sigma and his tiny, tiny head twice. Ditto for X4, but then again that game expects you to play it as both X and Zero.
Now for the achievements in the second collection. First up, "Out of the Frying Pan" for X5. I managed to get the Enigma to work in four attempts—the first of which involved firing it with just three out of the four parts, the other three had me reload and play Shining "Izzy Glow" Firefly's stage (which isn't particularly short) over and over. I guess you could say I was extremely lucky, but regardless, having an achievement based around RNG is stupid. There's also the one where you have to obtain parts from all eight of the Mavericks by getting a game over a certain amount of times to get all of them to a high enough level, as well as the one where you have to dodge all the lasers in Zero Stage 1 without using Dark Hold. The former showcased one of the biggest out of X5's many, many bizarre design choices, while the latter was a bunch of trial-and-error bullshit. X6's achievements were a pain in the ass to obtain, but mostly only because X6 itself is a pain in the ass. As for X7, the one where you have to save all the Reploids can go fuck itself, and so can the Alia one. I didn't get the Alia one the first time I played through the game, so I was convinced for the longest time that I had to replay X7 to make sure I went through all the conversations. Turns out, that achievement also counts the calls made during the intro stage by Axl (?), so while I didn't have to play very far the second time for it to appear, it's still a bullshit achievement to try to obtain and the worst one across both collections by far. The last achievement I ever got involved playing as all the Navigators in X8, which took a very long time for me because they had the infinite metal glitch removed and so I had to grind.