I first fell in love with Puyo Pop when it was known as Kirby's Avalanche way back on the SNES, and it's been a favorite ever since. (This game has been around for years and years under one title or another, though it's more well-known in Japan.) One reason behind my affection for the little colored blobs is that I see Puyo Pop as a flawless example of the correct way to design puzzlers. The core essence of the experience is utterly pure, yet it can be played with deep, elegant strategy that rewards quick fingers and even quicker thinking. Like Chess, Puyo Pop is one of those classics that takes a minute to learn and a lifetime to master.
Gene's done a fine job on his review, and there's really not much I can add. Puyo Pop is the not the kind of game that you can talk about at great length (a trait common to the entire puzzle genre, really). The game just is, and you're either with it or you're not. I definitely count myself on the side of being with it, and I'd bet that the vast majority of puzzle game fans who give it a chance it will be, too.
As for the game's flaws, there just aren't any. There's not a single thing wrong with this game; no rough spots or missteps that bring the cart down in any way. It may not be the type of mindblowing title that will change your perspective on life, but I'll be damned if I can poke any holes in it. We're talking solid as the proverbial rock here, people. For gamers who like their puzzles on the go, Puyo Pop is an essential purchase. (And for those who don't own a Game Boy but still want to check it out, Sonic Mega Collection for the GameCube comes with Dr. Robotnik's Mean Bean Machine, virtually the exact same game with a few cosmetic changes.)