When it comes to the Super Mario series, some games are good, MANY are great. It's not blind hype or fanboy bullshit, Super Mario is THAT good, even when compared to more innovative games (like the re-emerging Rayman franchise). As such, what should be considered a shitty game in any other franchise, is just a slight blemish in this series; not "great games", "good games". Spin-offs are another story but, right now, let me tell you about the core series, because even Mario has had some bad days.
1 & 2) New Super Mario Bros. 2 & New Super Mario Bros. U
There's nothing wrong with doing the same thing over and over again, but these two games really push it. Between New two's coin collecting gimmick and New U's reliance on nostalgia and familiarity, they would have been better off as enhancements to their last-gen counterparts. Hell, they were even released in the same year, if that wasn't any indication to how lazy these games were.
3) Super Mario Land
If this game was to be remembered for anything, its spawning the far-better sequel, 6 Golden Coins, introducing Princess Daisy, and eventually spinning off the Wario series. Otherwise, this game, even by portable standards, would have been simply a time-waster. A very short time-waster.
4) Super Mario Bros. 2: The Lost Levels
Much like the last two entries in the New Super Mario Bros. series, this game was too similar to the original Super Mario Bros. Unlike those games, Mario 2 offers new items and more challenging gameplay. Nonetheless, it was replaced by the reskinned Doki Doki Panic, nowadays referred to as Super Mario Bros. USA.
5) Super Mario Sunshine
Remember, "good" game, not shitty game. But still, FLUDD. If there's any reason why some people didn't like this game, you bet your ass it was because of FLUDD. Hell, I still resent that overgrown Super Soaker-knock-off for almost messing up my game in Super Smash Bros. Brawl, then having the nerve to show its shit in the sequel. Nonetheless, it was a minor hinderance on, what was other wise, another good game.