Because Metal Slug is still a kickass series that gives you more action than you modern day wusses can handle! MS is a real man's action game! But, if you're too used to original and evolving game series like MADDEN and Call of Duty, where every new installment is completely different, then I can see how the variety of action, strategy, and and survival in Metal Slug can be too much for you.
1200pts is a bloody steal for this game, it would have easily been a disc release last gen, and still was in the portable space. You get a game of perfect length that's meant to be replayed, with multiple routes through each level, lots of secrets, and an in-depth combat school that'll keep you busy for a long time.
Oh, and the secret of the game is to not hold the right direction while occasionally tapping the shooting button and the start button to constantly continue!