I was very, very excited to receive Super Paper Mario for my birthday. I've been a big fan of the series (of Mario RPGs) since the first Paper Mario, and the gimmicks in Super Paper Mario looked really clever.
When I got the game and started playing, I was still excited. The sideways controller felt great, and a few of the early levels are duplicates of original SMB levels, only now in three dimensions (sort of). It was brilliant!
As time went on, though, it got less and less fun. There was extensive backtracking, but unlikely Metroid, it was a hassle, not a joy. Worse, at one point, after a long series of backtracking, I had to enter "please" on an on-screen keyboard about five times. Why? Just because.
As more pixls (magic helpers) and heroes join your party, you have to switch between them. This requires going to the menu (by hitting "+" which is not right under your finger as you play), moving through options, and selcting one. If you need to change both hero and pixl, you need to go through the menu twice. There's a one second (or more?) delay when you switch. In some levels, you must do this constantly. Why isn't this fast, and mapped to something painless like trigger-plus-direction?
Chapter 8 is almost entirely black and white line art, and with no depth of field, it can be very hard to tell what's background art and what's an obstacle in your way. As you progress through the chapter, which becomes more and more boring and maze-like as you go, your other party members leave you. That means that if you get sick of it and warp to another level -- one of the fun levels -- you're screwed. You can't solve puzzles that require anyone but Mario.
I hope they make another Paper Mario game. I don't even mind the shift toward being more platformer-like. I just want it to be fun. The design problems in this game are far, far worse than I'd ever expect from Nintendo.
I found another reviewer who hits on a lot of things I can't bring myself to mention. It's at IGN.