A straight and forward tower defense game. If you like the genre, I very very highly recommend this game. If you don't like the genre, I doubt any game would be able to change your mind, and suggest that you carry on.
Defender's Quest managed to impress me by literally exceeding the average in every way I can think of.
+ Not a rehash of another tower defense game - it didn't really do anything extraordinary within the genre, yet I can't think of a single game I'd call it similar to.
+ Holy ♥♥♥♥, the story is actually good, the characters fun, and the funny parts actually funny.
+ There is no ultimate strategy that works for the game (build/upgrade order, etc). Each map forces a new strategy based on the availability of locations to place your characters, and enemy monster types.
+ There are dozens of maps, with 4 different difficulty settings, all of which have a New Game+ version which play differently. This game will take many dozens of hours to complete.
+ The music is good. Nothing spectacular, but for the genre and the pricetag, exceeds standards.
+ Lots of things to play with in the options menu.
+ Family friendly - I would see absolutely no problem in an 8 year old playing this game.