Defend Your Castle: A Must Have Wii-Ware Title
The fact that it has four player multiplayer action and a fairly good amount of replay value is good enough for a measly $5!
On a downside, the game does get repetitive, but it will drive you to play it just for the fact of: "How far can I get!?" When you play the game with multiple people the game gets harder and it also increases its enjoyment!
Do you really want to get Final Fantasy? A game which actually costs around $40 to unlock all of it's content, thanks to "pay2play". Or are you thinking about getting Lostwinds? A game that only takes 3 hours to beat and has no replay value.
Without question this game is worth $5.