This is one Disney game that is great fun and offers a good challenge.
For the most part it follows the storyline of the movie, where Simba is a young cub enthusiastic about becoming King when he's older, and his evil uncle Scar is determined to rule himself, even to the point where he eventually kills Simba's father. However there are some levels in the game which don't appear at all in the movie, such as Be Prepared, which is a lava level that Simba never went into in the movie.
You play as Simba, starting out as a young cub and later on in the game as an adult lion. The game is generally a platformer, so running and jumping are more or less the basis for the game. There are enemies, namely hyenas later on in the game, and as cub Simba you can only really jump on them since he has no attacks and his roar, for the most part, is useless. Adult Simba however can slash enemies, which comes in handy.
There's also little bonus stages with Timon and Pumbaa; with Timon you have to get bugs and avoid the spiders, and with Pumbaa, you have to catch all the good bugs that Timon drops, avoiding the bad ones.
The music seems faithfully composed to the movie, namely where I Can't Wait To Be King and Hakuna Matata are concerned. The graphics are also very nice.
Overall, this game is a really excellent little platformer that seems to capture everything that made the movie so great. The game is difficult, that much cannot be denied, but it's still fantastic and one of the best Disney-related games I have ever played.