Mega-Spider
Smash Ace
The beginning is what turns people away from X3, especially if you've played the first two X games. I feel like the developers should have decided to go for more challenging level design rather than make the enemies hit harder, but that's just me. I hate Kaiser Sigma myself, but I actually hate his first form more (which I call "Captain America Sigma"). His fireballs, despite being pattern based, seem random a lot of the time, and are annoying to dodge.I actually liked X3 a lot. A lot of the levels were fun to revisit. Not to mention it had some cool stuff in it like the Vile stage and the Gold armor. Still, the amount of damage you take in that game is a little much. And Sigma is really annoying.
I still prefer X1, X2, and X4 over it. But I found X3 to be way better than most people were making it out to be.
I like X2 more than X3 too, but X3 improved some things from X2, especially the Heart Tank placement. While X2's and X3's soundtracks have music pieces going for them, they can't beat the first X game IMO, especially in instrument quality. I don't know why the quality of the instruments dropped, which was incredibly jarring when I played X2 for the first time. As for the PSX version, I've only went out of my way to listen to Crush Crawfish's theme. I like it, but there are times where the quality goes from too quiet to normal volume. I'm not sure if that was the YouTube video I was watching it on, or it really is that way.One of the first things I noticed about the game was the odd selection of special weapons. I don't know about anyone else, but they just felt extra weird compared to the other games(though I did enjoy using the Spinning Blade a lot). Many of them lacked the potency that one would expect them to have(even some of the charged variants).
As for the overall difficulty, it was a step up from X2 but nothing that was too much, even early on. Though taking on the two Doppler Reploids without any special weapons or healing support can be pretty rough. Well, not so much for Byte, whose attacks are pretty straightforward, but Bit in particular with his paralyzing/homing shots. And you have no idea what stages they show up in. Other than that, X3 isn't really hard once you get used to everything, even the "harder" parts of the game. Not to mention having all of the upgrades(Hyper Armor/Gold Chip/Z Saber)makes things very trivial.
I once thought X2 had a better soundtrack than X3 after my first playthrough of the two games, with me thinking X3 had the weakest soundtrack of the entire series(barring X8 which I haven't played yet). But after actually listening to X3's soundtrack I realized it was far better than I'd given it credit for. Now I consider X2 to have the weakest soundtrack of the series. While X2 has some stand-out tracks, I don't think they can match X3's.
While we're on the topic, have you listened to X3's PSX soundtrack? The MMX Collection has the PSX version of the game. I've eventually listened to both versions of the soundtrack and got the impression that more players prefer the SNES version as opposed to PSX. Now I don't know if that's true, but I prefer the PSX version. I think the more powerful hardware did wonders for the musical quality.
But all things said, I like X2 more than X3.