If you can get past the short length and easy difficulty, then BIONICLE HEROES is actually a fairly immersive game.
The game is divided up into six different element-based parts of the island, which in turn have seven levels; 6 to get the first two mask evolutions (first Mata then Metru, for those of you who are interested) and then a boss battle against the piraka of that particular element. The gameplay itself is actually pretty good. You use the touch screen to aim and switch weapons, the D-pad to move, "R" to shoot, and "L" to use a mask power (if applicable; some mask powers take effect through immunity to something or being able to destroy barriers, sometimes both). The controls are nice and tight, and you can adjust for using your left hand.
The graphics are pretty nice looking, but the environments are very repetitive. Usually it's not such a big problem, but in the ice level, it can get pretty annoying. You have a nice selection of enemies that span a large amount of the BIONICLE universe including Rahi, Bohrok, Rahkshi, Vahki, Visorak, and, of course, Piraka.
The difficulty and length are where it starts to fall apart. It really is a very easy game, and obviously meant for younger children. If you die you just lose your current TOA bar (a sort of super power that you can use to become invincible) and have to start another one. You'll be at basically the same spot, perhaps a few steps back, with the same amount of enemies. This game will probably take you five hours to complete, but there is surprising replay value. First: there are BIONICLE runes that you can collect in order to unlock cheats. These include the usual invincibility and unlimited ammo, plus some gimmicky stuff like a gun that shoots barnyard animals. You also have some areas that you can't get to until you have a particular weapon i.e. you can't go under water until you have the water TOA's mask.
Overall this is a pretty fun game for fans of the toys, but falls a bit short when it comes to wide appeal. If you're a BIONICLE fan, then i'd say it's probably the best BIONICLE game on the market, but if you're just a casual gamer, then I suggest getting Metroid Prime: hunters instead. (and as a side note: the game does have multiplayer, but it 's multicard, so I haven't gotten a chance to check it out.)