I never played the gameboy game but I had the playstation game (I still do . . . somewere . . .) it's just like the TV series in that the animorphs never actually morph (when they do their signature morphs are at least present . . . except Marco, who morphs a rhino) you spend pretty much the whole game as the exact same little 3d character (with different colors to indicate which character you are) listening to poor one liners and jumping from platform to platform because the Yeerks really like platforms? Your morphs are completely the same, the grizzly doesnt take or deal more damage than the tiger, the wolf isn't any faster than the rhino so other than the colors of their clothes and the appearance of the animal you get to morph the animorphs themselves are pretty identical, the only difference I've noticed is that Rachel flips when she jumps . . . I guess that's variety.
When you do morph you have like twenty seconds (not two hours) to do whatever you have to do in morph before you're trapped and . . . commit suicide? You can only morph right before a fight and can't demorph until the fight is over so the action in the game where it exists needs to be over in 20-40 seconds, I like to think this is why the Animorphs are so reluctant to spend more than a few seconds in morph in the TV show, Elfangor set the timer wrong when giving them their powers so instead of two hours they have two minutes . . . mostly you dodge giant traps that, in a real three dimensional world the animorphs might just . . . you know, walk around, or morph into something to fly over it . . .
All that said I actually enjoyed it (I know . . . wierd) you get to be whomever you want (provided you don't want to be Ax or Tobias) take on Hork-Bajir that actually resemble (almost) the book Hork-Bajir not those disgusting rubber chickens from the TV series, I'd actually say that playing the game is more entertaining than watching the TV show, except for the fact that it gets very annoying due to how easy it is to miss a jump and die. You'll fall off the platforms again and again, especially in the Gardens where there are giant flipping fans which either dice you or blow you off your platform (Why, Visser Three, why?! I mean I knew you were evil but this is just . . . evil!) be forced to watch that lame "game over" movie which shows everyone getting infested (including whoever you played as, even though they fell off the screen to their death . . .) until you can see it in your dreams.
Still it's neat. If you ever get a playstation or ps2 (garage sales ftw) this is a game easily worth an hour or two of laughs . . . and about fifty hours of cursing and demanding to know who installed giant fans and bottomless pits in The Gardens . . . I might go looking for the game now just for nostalgia.