Regardless if it's a US or Japanese one, edutainment games have always been a hit-or-miss platform. Despite every effort to make it as entertaining as possible, several have resorted to cutting out the quality and settling with just presenting the main subject, which in turn makes it too academic and therefore less fun for people like you and me. Still, there are a few noteworthy ones that were able to pass the message along without leaving hardcore gamers high and dry.
Kotoba No Puzzle: Mojipittan is one of the few successes in that respect. It was not just able to make it as an effective edutainment game, it created a nationwide craze in Japan that continues to persist up to this day. Mojipittan started out as a nondescript arcade puzzle game, but has become so popular that many versions have been released for various systems like the PS2, Wii, DS, PSP, and even mobile phones. The secret lies in it's innovative gameplay mechanics and hypnotically addictive background music.
I never thought that Toradora would come out as a galge, but lo and behold, here it is. Toradora Portable! puts you in the shoes of main character Ryuuji Takasu, who has lost most of his memories, even those of his relationship with resident tsundere Taiga Aisaka. Thankfully, despite the amnesia, he hasn't forgotten his cooking skills and the obsessive-compulsive desire to clean any mess he sees... conditioned reflexes, I'll be bound.
Rena Ryuugu's at it again. In her never-ending quest for finding cute things to take home, she comes across a mirror in the Hinamizawa Village dump site. After showing it to her friends, they find out that it has the power to grant any wish. So as usual, a fight ensues with possession of the mirror as the top prize...
Higurashi Daybreak Portable Mega Edition is actually a sequel of Higurashi Daybreak Portable, the latter being a port of a popular doujin game for the PC. Battles are conducted in a similar fashion to the 2-on-2 Gundam Battle series, so anyone that has experience with the aforementioned will have no trouble adapting to this game.
Yes, I'm also a fan of Lucky Star. A BIIG fan. This game is one of the reasons I decided to get a PSP in the first place. While Kadokawa Shoten's Lucky Star: Net Idol Meister isn't what I was expecting it to be, I gave it time, and my patience was greatly rewarded in more ways than one.
I came across video of the game Planetarian ~Chiisana Hoshi No Yume~ in a forum I went to, and it certainly had me curious. The design for the female character was superb, and it was made by Key, known for their popular galges (Kanon, Air, Clannad, etc). As soon as I started the game, it utterly shocked me. I sat through it in one night, and it still haunts me up to this very moment.