Super Paper Mario is a very important game in the PM series. Both for good and bad reasons. With TTYD, I think they felt they hit a wall, or rather, a plateau. They'd taken the PM formula and took it to near-perfection. What's left to do? The change from PM to TTYD surely can't be replicated. "Screw it," I imagine some feisty young employee saying out of turn at a meeting, "let's not try to make TTYD2. We've got all these incredible news ideas. Let's just go all out." Silence. And a nearby senior says, "you know what? I agree. Screw it."
SPM is truly ambitious compared to any other PM game. The whole thing feels like a gamble - what if we change this and that? The art style was unlike any other PM game, or game, period. Many mocked the shapes approach to character building, but it gave the game a very unique aesthetic that made it feel like it was taking place in a universe beyond that of previous Paper Mario entries, or even SMRPG. I can't say it always turned out well (see: the townsfolk), but it made the entry itself artistically identifiable.
The story was a gamble, too. The Mario RPG games have always been commended for having good writing and interesting characters. How about investing more in the story? They give us this weird, interdimensional tale of romance and angst and sacrifice. They really amped the stakes up, too. The consequences of failure in PM were no wishes for the Mushroom Kingdom. The consequences of failure in TTYD was a world under the tyranny of the Shadow Queen. The consequences of failure in SPM was the destruction of all dimensions. There's no way out! You can't hop to another country or planet - it's really game over if you fail. And SPM gives you a taste of this by showing you what awaits existence if you don't buck up in Chapter 6, where you watch a lively little warrior dimension get reduced to nothingness. The story is grandiose, and it tries to hit you hard in the feelings. Once again, it may not be your cup of tea, but they had lofty hopes for the story.
The gameplay is probably the biggest gamble they took, and arguably the one that didn't pay off. The PM games had a very well-loved and unique combat system that was suddenly replaced by platforming with oddly incorporated RPG mechanisms. If you liked PM's gameplay and wanted to play a game like that, you had no choice but to play PM1 or TTYD, because no other game played like that, not even SMRPG or M&L. You can imagine the frustration of having this unique gameplay changed for something entirely different that maybe didn't work. But once again, this was not a half-baked attempt at gameplay change (unlike, say, Sticker Star, which took the unique combat system and removed a lot of features and added some new ones nobody wanted and said "THIS IS IT"). This was an overhaul.
I feel like there were really high hopes that this game would do well. All the changes to this game from TTYD are bold, perhaps experimental. They weren't always the best, but I feel like there was real love in that game. I can imagine the disappointment when it failed to live up to expectations. And that led to the absolute bottom point of the series, the much-maligned Sticker Star, which is SPM's opposite in every way. Is the story too big and crazy? Let's have a very small, traditional story that we know the beginning and end to. Are the graphics unusual? Don't worry, we're going back to the old style. In fact, we're going to draw from the mainline Mario games and remove the RPG-original characters so that you only see familiar faces. Even the enemy Koopas will be friendly-looking! Didn't like the gameplay? We'll go back to turn-based combat... but make it unrewarding and unfun. I really have no explanation for this one other than the freaking Nintendo Gimmick Ghost haunting some developer.
And the bizarre part is that despite the mediocre reviews and general outcry from fans, Mario and Luigi: Paper Jam follows Sticker Star's lead. No new characters. Same old plot. A weird fetish with the paper part of Paper Mario, as if that were ever the most important part of the game. At least Bowser talks now, that's a step up. And to be fair, it is a Mario and Luigi game, not a Paper Mario game. But it's disappointing to see the path Paper Mario might be taking. Maybe it works, supposedly Sticker Star sold very well. But it feels soulless compared to the first three games, which were really something special. It's playing it safe in the places it shouldn't be (the plot) and taking unnecessary risks where a lot of fans want the old style back (the gameplay).
And I bet you Sticker Star wouldn't have happened... if Super Paper Mario hadn't. Sticker Star is in every way a reaction to the excesses of Super Paper Mario. A lot of fans considered Super Paper Mario awful before Sticker Star came out, and it was usually considered the worst of the Paper Mario games. Now that Sticker Star has occupied that bottom slot, reception is a little better. But there's still some resentment that this weird game came along and ruined our perfectly good series, and resulted in the reductive Sticker Star that, unfortunately, appears to be sticking.
The unpopular opinion part is that I don't resent Super Paper Mario's excesses. I appreciate that it tried to be something more than what everyone expected, something more than the rehash that would eventually come. Gameplay-wise, I don't think it lives up to PM1 and TTYD, but I enjoyed playing that game. The plot and characters, ridiculous as they could be, still have that charming humor that characterizes PM games - plus, it gave us Dimentio. The aesthetic got a bit elementary at times, but when it worked, I thought it was gorgeous, and it really made the game seem refreshing. Otherwise they'd have gone with recycled TTYD assets (which they did where they could), resulting in a less visually distinctive game. I really wish Super Paper Mario had worked. I don't think it would have led to a string of platformer-RPGs. I think it would have given the folks at IS the freedom to keep experimenting with the games. Instead the Miyamoto hammer came down. Fans resent Super Paper Mario as the beginning of the Dark Ages, when I view it as the last entry in the Golden Age.