Well, there's one of the Parodius games that require one of the special chips. Also Metal Combat, but that's a Super Scope game (so unless you game on a CRT...).
As for Mega Man X2 and X3, there's always Mega Man X collection for PS2, which I believe is still cheap.
The 2 Kirby games listed are on the Wii Kirby collection.
So if you game on other systems, you are not missing a whole lot (Mario RPG being the most notable title).
I have to admit that Doom and Street Fighter Alpha 2 are both just technical feats, and better enjoyed elsewhere. But I totally get the appeal; I own both, and still plan on trying them out on my SD2SNES (or FXPak or whatever it's called now).
My SD card I was using for my SD2SNES doesn't save or erase anymore, so I'm using it on my cheapo Super UFO Pro 8 (loads firmware from the cart and uses a save battery, so long as you only play through one save game at a time). It's in my beater system (shell of the system is yellow and all cracked to hell, and I kind of like it).