I bought this game for my 4 years old son who is learning to read and knows most of his alphabet. A few months ago I bought him the Jedi maths game which he really likes.
My son has only done the first level so far and it was bought so he had a game which was more word focused as many of the others he has are number based. He also has SonicX, Wall-e, Spongebob, Dora, seaside quest and Outwit.
It is one of his favourites at the moment along with Jedi Maths, SonicX and Spongebob. It is helping with his letter recognition although I think the game play is more interesting in Jedi Maths.
My son also has a DS and other electronic games which he likes to play from time to time so his Leapster is only played a couple of times each week but at least it has some educational content.