Let's party like it's 1987.
Contra 4 is your basic 2D platforming run and gun type 2D side-scroller. You can jump, run, and shoot. Simple, and yet the toughest game to conquer on the DS as of now. Blasting your way through 7-9 levels with infinite ammo and the ability to hold two guns simultaneously has never reached a high like this.
Konami has stayed true to its roots in this iteration of the series, which is a good thing. Arcade mode is not different from any previous games in the main series; in fact, some music, bosses, levels and enemies were ripped from older Contras. Nostalgia anyone?
Despite the simple concept and an arcade mode that only consists of less than 10 levels, Contra 4 is far from being a short game, and its learning curve isn't necessarily immediate. Later boss levels, 3D missions and a unique ocean level offer different tactics and sometimes controls, which ultimately makes the game better. New weapons affect the game largely (the pea shooter barely deals any damage, which forces players to constantly be on the lookout for better weapons — what makes the game very hard is that if you die, you lose your upgraded weapon), and the variety is good. And if you haven't realized by now, the Contra series is hard. This is perhaps the hardest in the series, which means you'll be re-trying the arcade hundreds of times to get past normal mode -- making the mileage for your money pretty high. Multiplayer requires two carts, but if you find a friend with a DS and a card, get ready to kick ass on a game that seems much easier than its single player counterpart.
The bonus features are plentiful and extremely entertaining. Fun, short missions with varying goals - and great rewards. Contra 4 is an arcade shoved on a portable system; it's fun to be able to pick it up and play through the Challenge Levels on the fly (beat the game on easy to unlock the challenge levels). Their short length makes the game much more portable.
The soundtrack is great, and veterans will definitely recognize a few memorable tunes remade for Contra 4; another success of a soundtrack from Virt.
Overall, a rewarding game whether you played the older Contras or not, and some of the best $15 I've ever spent in video gaming. If 2D platforming isn't your thing - or you're more casual about gaming - I'd suggest you avoid this; but if you're anyone else, this is an excellent game in an excellent franchise.