Hmm. The Ultimate Kana Challenge is a completely different type of game. You have to click the kana in order (a, i, u, e, o, . . .) while they're all moving around the screen. This can be helpful, too, but I think I prefer the random drilling of the Slime Forest RPG.
Slime Forest can help with kanji, but it depends on what sort of practice you want. As I said, it's only meanings, not readings, so you get things like "person" instead of "hito" for that kanji. A nice thing is that they try to give you reminders that will help you associate the kanji's shape to its meaning. I found that helpful, and I think a few of them have stuck with me even though I haven't played the game or practice with the kanji for quite some time.
FWIW, I've downloaded and tried a number of other games/programs for learning. Some are more like kanji dictionaries for reference, but others are games like the couple mentioned here. These are a few more game-like programs you can try if you like.
Knuckles in China Land (http://chinaland.cjb.net/
) is another RPG
Kanji Trainer Penpen (http://www.coolest.com/penpen/
) which the site calls Tetris-like in that things move and you can't stop them
Learn Kana (http://physics.uwyo.edu/~brent/jal/brejal.htm
) is a flash card program
Dream Kana (http://www.dreambreed.com/software.html
) is a similar flash card program, which I don't have, but found when looking for the Learn Kana web site