Super Metroid should be an EXTREMELY top priority. A difficult, yet satisfying game, with epic boss battles, great music, awesome graphics (for 2D, obviously -- personally, I love 2D the best, though, so that's actually a plus for me), and great replay value. Also, there are "advanced techniques", using Smash Bros terms. Single Wall Jumping and Infinite Bomb Jumping, just to name a few. That can add extra time, to use during your runs through the game or just to practice and learn for the heck of it. Then there's sequence-breaking (getting something before you're supposed to, or getting past an area you're not supposed to be able to yet -- for example, using a trick in Brinstar, you can get a Super Missile tank before, or without, fighting Spore Spawn to get the official item) to add even more replay value. And to top it all off, it's a Metroid game, so speed running, low percent running, and 100% running are all great options to add even more to the experience.
Plus, the environments are so diverse, creative and awesome that it only makes it better.
It's my favorite of the three (
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) SNES games that I own. It's also probably my favorite game ever. DKC2 is also great, as it has been said. And yes, its music is awesome.
This sums it up rather well, especially #1.
DKC1 is also good, although not as good as the second in my opinion. I haven't played 3, but from what I've heard it's not really much different from 1 and 2. So if you really like the first two, 3's definitely worth it but it probably shouldn't be a top priority.
I don't physically own A Link to the Past for SNES (I have the remake for GBA and I have it for Virtual Console, when I have some extra money to spare and I don't have any other games that really need to take precedence I'll get it for SNES), but I have played it and it is AWESOME and definitely worth your money.
But yeah. The SNES is arguably my favorite console; the only thing it could be seconded by is my Sega Genesis, and while that has great games going for it it also has some nostalgia going for it, having been my first game console or platform in general.