Kimchi-man is pretty crappy overall. Rally Pop is like a very crippled game of Worms. Dungeon and Guarder is a good, fun game, but its' overly difficult. Tomak is also a nice game, but is a little too short (but a good JoyGP purchase). Tanglees Magic Squares is a worse version of Yoshi's Cookie (just play the ROM of that game instead). Dyhard is shitty overall.
Now for the games I like:
All For Princess - Fantastic game. Tons of moves, nice controls, great graphics/sound. The only thing I've never seen anyone mention is the AI.. it's terrible. Enemies rarely attack you. They tend to just sit and take a beating. Still great, though.
Little Wizard - I don't see why people don't like this game more. Sure, it could have used more animation, but it's got really nice graphics and is presented very well. The lack of moves isn't as dramatic as reviews would make it seem - each character has a nice set of moves. One thing I enjoy about it is that it has a really frantic pace. It's a fighting game that makes you sweat. Reminds me a bit of Pocket Fighter. Good stuff.
Pinball Dreams - A perfect conversion of the Amiga game. Everything's there. Nice tables - good video pinball. Don't get it if you really suck at pinball, though, or it will just piss you off, no matter how good the game is.
GP Fight - Frustrating fun. It's a pretty frantic game, the AI is pushy, and there are some cheap hits here and there, but it's got a lot going on. The levels are extremely varied in what you have to do (I love the swimming pool level.. very satisfying). It's difficult, but possible, and you get a weird sense of achievement when you come out on top. I haven't beaten it yet, so I can't comment on it's length. You'll especially enjoy the graphics if you like River City Ransom, Super Dodgeball, or Nintendo World Cup. It's an expensive Joy GP purchase, though, so think about it before you buy it, because you may not like it.