The problem with nostalgia—particularly gaming nostalgia—is that while you can easily recall all the happy, wonderful memories of youth, over time you forget all the pain and suffering that comes with being a dumb kid.
While Contra 4 retains the series' fantastic graphics, tight controls, and hyper-macho, shoot-first-and-never-ask-questions gameplay, it also retains the series' trademark insane difficulty. In Contra 4's world, it's not enough that you have enemies constantly attacking you from every direction with guns, knives, and sharpened body parts, nor that you're asked to fight bosses that are literally 40-feet-tall piles of semi-human remains—no, Contra 4 also asks you to do all of that through nine huge, multi-tiered levels... without ever giving you the option to save your game.
If you run out of extra lives on the first level, unsurprisingly, you start again from the beginning of the game. But asking players who have reached the entire game's final boss fight to start over from the beginning after death? That's just sadistic.
If you can stomach the intense difficulty of the game, Contra 4 is easily one of the best shooter titles to see store shelves since 1992's Contra 3. It has excellent graphics, the sound is intense, the music is almost as stirring as that of the original Contra, and the developers find some really creative ways to use the Nintendo DS' split-screen dynamic. (Plus, they were kind enough to add unlockable versions of 1988's original Contra and its sequel, 1990's Super C—owning portable versions of these two classics is worth the admission price alone.)
If you're an old school gamer who grew up with the series, I highly recommend Contra 4. I'd also recommend it if you've got some sick fetish for repeatedly watching pixilated characters get shot. But if you started gaming anytime after 1990 and have a great self-image and a happy life, be warned that Contra 4 will cause you to doubt the existence of a loving god.