Wario Land II
Whatever else anyone wants to say about this game, there's no denying that it's unique. The central gimmick is that Wario is immortal, so no amount of damage will ever result in a Game Over screen, and allowing certain enemies to apply their attacks directly to Wario's forehead is often necessary to progress or reach secrets. It's a really interesting idea that the game uses well in most levels.
Those levels are the game's other strong point. You have varied objectives in each of them, from turning off an overflowing faucet to defeating four specific enemies hidden throughout the map. Each chapter focuses on a few different status abilities and does a good job of introducing them without a tutorial, although sometimes I definitely felt the game would've benefited from breaking its vow of silence and giving me a few interactable sign posts.
Unfortunately, I can't recommend WL2 because the only way Nintendo could think of to add difficulty to a game with an immortal protagonist was to waste the player's time. Wario can't die, but he can and will be sent back to the beginning of certain fights after taking a single type of hit, which is immensely frustrating and not at all fun. Another level about climbing to a rooftop plays like an early Getting Over It and can see Wario knocked all the way back to the ground floor if you take an unlucky hit. This might not be an issue for you if you're particularly patient and don't mind repeating content, but as someone who very quickly gets sick of doing the same thing, those scenes killed the whole game for me.
Oh, and the soundtrack is oddly weak for a Nintendo game. It's not bad by any means, but there wasn't much variety and I already can't remember any of the tracks.
Wario Land 3
WL3 is a confusing sequel. It abruptly changes the series from Roman to Arabic numerals and removes Wario's ability to buttslam and swim effectively. In exchange, it opens up the level selection so that you can replay old levels whenever you want and sometimes get a choice about which to play next. That said, it's still largely the same game, and I just wasn't feeling up to more Wario after the last title. I stopped after the third level.
I mentioned that this game's graphics were a horribly broken mess when I covered it originally, but I put it on the list anyway in the hope I'd find a solution. Unfortunately, I didn't, and it's really not playable when all the sprites except (usually) your own have their constituent parts randomly scattered around the screen. It seems like an adaptation of Super Mario Kart to GameBoy a few years before Mario Kart: Super Circuit tried the same thing, but I can't tell you how successful it is.
Survival/crafting games may actually be my least favorite genre when they're not named Subnautica, so I never really expected to like Survival Kids. I put it on the list anyway because the idea of a big sim like this on GBC is just fascinating, and in that sense it delivered. There's a robust crafting system here, even if I couldn't figure out how to tell it to rub sticks together to make fire, and it even simulates wildlife sleep cycles and food safety. It looked like there are some interesting environments after you get past the initial jungle, but I didn't see much of them before I got frustrated by managing meters and the incredibly short day/night cycle. Still, if you like this genre, it's probably worth checking out. There's certainly nothing else like it on GBC.
A mahjong game where it's really hard to tell which tiles are on the same level because of the limited graphics. I'm honestly not sure why I put this on the list - there's a certain base satisfaction to playing this sort of game, but other than that Shanghai Pocket itself isn't offering much.
SD Hiryuu no Ken EX
A 2D fighting game with a full arcade mode and (I think) link battles. It's actually a pretty robust fighter with a huge cast of characters who all seem to play reasonably differently and movesets that make use of quarter circles, etc, to expand the utility of the GBC's two buttons. The stages are all identical in a gameplay sense, but there are a ton of different backgrounds and some of them actually look quite impressive for the system.
The main drawbacks are that there doesn't seem to be anything explaining your character's moves or a way to learn combos, and more importantly, I can't imagine being able to see what's happening on a tiny GBC screen. Character models are quite small and I had trouble making out moves even with the screen blown up to many times its original size. You'd need to play this with a magnifying glass on original hardware.
Now that said, if you're a big fan of old 2D fighting games, I think it's worth playing this one just to see how much they managed to cram into a GBC cart. The language barrier is a non-issue even if you can't read any Japanese because there's hardly any text that isn't just flavor.
Current status of the list: (Good games are bolded, green means finished and orange means abandoned. Bold means a game I'd recommend today)