Contra III embodies the best and the worst of old school side-scrollers. One on hand, its a frantic, tense, and gleefully destructive game that has you using all manner of weapons to battle all manner of aliens. On the other hand, its ridiculously hard: you die in one hit, and the save system sucks. Its possible to overcome the difficulty, but it involves so much pratice and memorization of enemy weaknesses that it comes very close to being not worth it.
Bottom line, its a very fun game, but its nowhere where the Super Metroid or Super Mario level of classic.