I know what you're thinking. "Best in the series? Pfft, there's no way." But in my honest opinion, it is indeed the best. Why? Well that's what I'm here to explain to you.
WARNING: The below passage may contain spoilers.
The Paper Mario series has always produced some of the best Mario games of all time (that is, until the fourth game came out but that's another rant), and this game is definitely no exception. It has a beautiful story, a nice, simple art style, satisfying gameplay, and amazing music.
The story takes place in another world, separate from Mario's Mushroom Kingdom. There is an ancient prophecy that predicts the end of all worlds. Mario is prophesied as a legendary hero who is the only one who can stop the destruction of the multiverse by the hand of the new villain, Count Bleck, and his five minions. The four playable characters are Mario, Luigi, Peach, and even Bowser, each with their own abilities.
The gameplay feels smooth and satisfying. Mario has the ability to switch between 2-D (default) and 3-D (the stage flips to the side, revealing the third dimension). This can be used to go around obstructing walls and avoid nasty enemies. Princess Peach has the ability to float over large gaps, similar to her abilities in Super Mario Bros. 2. Luigi can unleash a mighty Super Jump to reach higher places and attack high enemies. Bowser is able to breathe powerful flames to burn away enemies and other obstacles such as a door covered in dried bark. He also has double the attack power of other characters.
They can all jump on enemies and use Pixls, fairy-like creatures found in various chests throughout the game. The main Pixl, Tippi, can give helpful hints and bio various enemies to help you defeat them. The other Pixls grant abilities such as Ground Pound, Hammer, Barrier, Bomb, and more. Unfortunately in some instances you do not have access to Tippi and the other Pixls (such as one part where one of Count Bleck's minions separates you from them). In these instances you must rely heavily on flipping into 3D and other character abilities to survive.
The item system works similarly to previous Paper Mario games, you have the standard healing items and attack items. You also level up by defeating enemies and earning points from them. Leveling up increases your max health and attack power.
There are eight chapters in the game: Lineland, Gloam Valley, The Bitlands, Outer Space, Land of the Cragnons, Sammer Kingdom, The Underwhere & The Overthere, and Castle Bleck, the Count's main base. The hub world is Flipside, a rather large town with inns, shops, fortune tellers, and a mirror-image counterpart called Flopside. Merlon, the sage who wields the prophecy of light, also lives here.
The story gets deeper throughout the game, and by the time I got to the final boss I found myself loving every bit of it. Count Bleck (spoiler alert) isn't as evil as he seems, and was only acting out of grief for a lost loved one. One of his minions, on the other hand, is playing the entire cast for fools and is the true final boss of the game. I will not say which one, so as to avoid further spoilers. But the ending of the game in which Count Bleck is reunited with his loved one brings a tear to my eye and really shows how the power of love can counteract a prophecy of destruction and evil.
Overall, Super Paper Mario is not only my favorite Paper Mario game, but my favorite Mario game overall. I would rank the series Super Paper Mario>The Thousand-Year Door>Paper Mario>Sticker Star. When Sticker Star released and had a generic "save the princess" story and no new characters or returning Paper Mario characters, it made Super Paper Mario look even better by comparison. I rate this game 10/10 and hope for a true sequel. Because damn, this game sure does deserve it.
During the ending of the game, when Mario, Luigi, Peach, Bowser, Merlon, the Pixls, and Count Bleck's remaining loyal minions all gathered on Flipside Tower to say their farewells, with the beautiful song "Proof of Existence" playing in the background, I shed tears every time. Such a beautiful game with a beautiful message. And when the narrator closed with "May we meet again in another time and place," I just burst into tears because that implied sequel never happened due to all the butthurt fans criticizing this game for not being exactly like its predecessors.
I applaud the developers of Super Paper Mario for creating what to me is the perfect blend of Mario platforming and deep, touching story. May we truly meet again in another time and place.