We should leave this thread stickied and keep updating it...
Super Mario Land - Honestly my favorite out of the original GB Marios... like the level design and especially the music the best. Even if it doesn't look all that great graphically.
Super Mario Land 2: 6 Golden Coins - A stunning improvement in terms of graphics over the original, but the music sucked and the majority of the game was a cakewalk with bland level design (even if the ideas for levels - a giant Lego Mario, a pumpkin haunted land, outer space - are much cooler than most Marios) up until the awesome and really challenging final boss.
Wario Land: Super Mario Land 3 - Pretty easy game with better level design than 2, but the music is horrible and Wario always felt a bit too sluggish to control as compared to Mario. Need to do a bit of grinding if you want to see the best ending, which sucks.
Suikoden Tactics - The graphics look like an N64 game, the story is silly as hell (cannons that turn people into fish men, wtf), but the elemental tile system separates this from your typical TO/FFT esque SRPG. The battles are long, draining, and challenging, with constant enemy reinforcements. But I don't like how there's permadeath for all of the optional characters. Still, I enjoyed this one more than 3 and MUCH more than 4, although as far as SRPG spinoffs go it ranks below both FFT and Wild Arms XF.
Emerald Dragon (SNES) - A pretty decent SNES RPG with a unique concept (dragon changing into a human to go to the world of humans to protect a girl he loves), an Ultima 3-ish battle system, decent production values (some full-screen anime portraits and some VA) and unfortunately WAY too many battles.
Faxanadu - Never beat this one back in the day but I finally did. Overall a pretty decent NES title, with catchy music and a big world to explore... but its got some frustrating enemy placements (like one enemy who attacks you as you slowly climb up a certain ladder, knocking you off, almost impossible to avoid), and some issues with backtracking if you're not precognitive (or not using a guide) and don't know what keys you might need to open up a door later in the level.
Wild Arms: Alter Code F - Ehhh, my least favorite of the WA series so far. An unnecessary remake of the original game, with a drastically simplified inventory system, and remixed tunes that aren't as good. It has a few additions over the original, like a ton of optional content (a few bonus dungeons, extra bosses, seed growing minigame, and the addicting-as-hell Puzzle Boxes), and several new party members. I'd stick with the original.
Terranigma - Beat it a while ago, didn't remember much about it, but came by a repro cart recently. Lovely game, I love helping to develop the world by reviving the continents, the flora and fauna, and then lead humanity into a golden age by encouraging trade between civilizations... High-concept game which also has some great action RPG mechanics. Some bosses are a bit of a slog though and require grinding.
Axiom Verge - Although it's a blatant Metroid copy, it still features a ton of unexpected twists and surprises. It's a game for the kinds of people who will play NES games even as they slowly start to glitch. A few of the bosses were bullet sponges with repetitive patterns, the only mar on an otherwise wonderful game.
Theatrhythm: Final Fantasy (unlocked all songs, all songs cleared with at least an S on Normal) - A fun rhythm game but pretty much obsolete thanks to...
Theatrhythm: Final Fantasy Curtain Call (unlocked all songs, all songs cleared with at least an S on Normal) - An insane amount of content providing for a ton of nostalgia. Still hate the character designs though.
Adventures of Lolo - Fun puzzler that I think I beat as a kid but felt I should replay. Made it through the whole game on a Sunday afternoon. Still need to get 2 and attempt to beat 3... the 3rd one is a feat I was never able to accomplish as a kid.
Rescue Rangers 2 - Great game but feels a bit like a re-tread. First one I think I prefer due to nostalgia... but still this was one of my holy grails for collecting and I'm glad I got to play it.
Gravity Rush (still need to do the DLC) - Frustrating camera and controls at some points, and a few annoying parts (like the battle with the hydra that made me give up on this game for a while before I discovered the trick)... but man is the art style stunning. Like a cross between anime and French bandes dessinees. Makes great use of the Vita and looks gorgeous on that system's screen.
Forgot a few:
Threads of Fate - charming as hell, with some great graphics for the era. Loved Mint's character in particular. Some touchy platforming elements and strange hit detection though.
FF15 Episode Duscae - still a work in progress, but I'd have definitely preferred a more traditional menu-based system. Love the setting though, the route-66 meets far-out fantasy of the demo is so unique.
Very close to the end of Kirby and the Rainbow Curse, Captain Toad, Mega Man Legends, and I made it to the end guy of Castle of Illusion Starring Mickey Mouse but I died last time I tried. Will hopefully beat all those soon but since I have a little bit of time before the big crunch at work, I'm gonna start and hopefully make headway into Type-0.