The first TMNT game for the NES was single player only, which was frustrating enough. Add in the fact that it was horrendously difficult, even for the very challenging standards of the time, and it left a bad feeling in your mouth. The second Turtles title was a port of the first TMNT arcade game, and a bad one, at that. The Manhattan Project had the same gameplay as it's predecessor, but it was an original story, and thus you were not constantly reminded you weren't playing a shoddy port of a superior arcade title.
4. Life Force
Konami made some of the best games for the NES, and the Gradius series was among the finest of them. Life Force took everything that was good about Gradius and added in 2 player co-op. The power bar was one of many innovations that were mimicked by many other shooters that followed. Swapping from horizontal to vertical scrolling mixed the action up nicely, as did the creepy graphics. Best of all, the Konami code worked here, giving you a full 30 lives. Trust me, you needed it.
I already covered this game for Co-Op Classics, but it still deserves more praise. The brilliant twist of combining RPG style statistics into the established brawler genre was quite influential; today, we see stats in all sorts of games, from FPS to sports sims. The recent videogame based on Scott Pilgrim Vs. The World is a pure homage to River City Ransom. One more thing: "BARF!"