It ain't.
Sunshine is underrated, though. Always said it. Blue coins are incredible and create for some of the best platforming in the series. Galaxy 1 remains the GOAT though. Every level rocks. Only Mario to have that level of consistency is Yoshi's Island. The rest of are quantity over quality.
Reality is that ALL Mario's? Half the game is shit.
Mario 1, half the game is a copy pasta.
Mario 3 has bloat bloat bloat.
Super Mario World is pretty consistent, and even that has some snore levels.
Yoshi's Island is perfect because it emphasizes quality over quantity, has less levels than other Mario games, and all of them are tied to a specific theme.
Mario 64, the game doesn't get interesting until like the third floor of the castle.
Mario Sunshine, lol. Warp levels and blue coins rock, but there's plenty of mediocre Worlds in this like the theme park.
Mario Galaxy has no issues from my recollection. Or if it does, it's the only one besides YI where I didn't really give a shit because I was having too much fun.
Mario Galaxy 2 is pretty boring. I beat Galaxy 1 in two-three days. It took two months to beat Galaxy 2. It isn't on the same level at all. Still good though, just as much filler as past games.
New Super Mario Bros. sucks.
Super Mario 3d Land is the epitome of horrific Mario "half the game is shit" design. First playthrough sucks and is boring as fuck. Second playthough is
Most inconsistent platforming series. Real talk. Most of them are bloat city. You just never noticed.
Honestly, if someone asked me what Mario games are worth playing? I'd say only World, YI, 64, and Galaxy were worth playing in 2015.Haven't played NSMBwii, wii u, or 3d World yet, so I definitely have Mario to catch up on, but I doubt they those games prove my hypothesis on Mario incorrect.
Castlevania is the series Mario wish is was. Castlevania > Mario