Two words summarize why this game's ratings are so high: VARIETY.
There is variety in gameplay. No two puzzles are similar. And each puzzle will require a great deal of creativity to solve.
Graphics. No two places will seem similar. Your character even changes appearance as you go through the game. In addition to this, you'll appreciate how much the developers have maximized the console's capability when you get to the part of ice cavern.
Again, no game is perfect. The game did lack variety in terms of combat. You would expect that you would be able to pull of more sophisticated combat moves as you go through the game. But the "bounce from the wall" is actually the best you can manage.
There's also not much variety in the enemies.
However, it's understandable since this game's emphasis is more on puzzle-solving rather than action. The battles just add a little more excitement to the game since killing most enemies is as simple as backing into the wall and performing the spectacular wall move.