Game developers will always imitate what's popular. In the NES era, it was side-scrolling platformers. In the SNES era, it was fighting games. Playstation brought us bad attempts at 3d action games and poorly made FF7 clones. Then it was FPS games, and now, it's "casual" minigame collections for the Wii.
The thing about these imitators is, they never imitate the aspects of the game they're ripping off of that made the original game GOOD.
Super Mario Bros. was simple and fun, and had a bunch of secret that anyone could find with a little time and luck. Rip-offs had bad controls and had "secrets" that you couldn't find unless you had a decompiler or days of free time. Street Fighter II had tight controls, and a gameplay system that made it easy to play, yet hard to master. FF7 had a halfway decent story and impressive cinematics. Halo had easy-to-use controls and fluid gameplay. Wii Sports had surprising amounts of hidden depth and endless replayability. Rip-offs have none of these.