yeah this game is a bit overpriced. It's still a great game and all, but to me it seemed too short and was hoping for an epic boss battle (although that had been explained in a humorous way).
But if anyone likes Metal Slug or Contra this game is still worth picking up, hard to say about the replayability, after either beating it 2 or 3 times (pretty short already beat it twice and ran through the first two levels with a friend) or getting all the achievements it doesn't feel like I would play it that often afterwards.
I also liked Eat Lead, and like how this game pokes fun at itself. Although Eat Lead did get repetitive towards the end. Guess the bottom line was I enoyed the first game, liked the demo of this and just wanted to support the developers.