My girlfriend bought me Sticker Star as my Christmas present. Here's an honest review. It's long. There aren't 'spoilers' or whatever in it, and anything I mention has already been plastered all over this thread anyway.
While I initially heard the whole "Miyamoto stepped in and ruined everything" thing (and frankly believed it 100%), I was in for an honest surprise. The game is great. The dialogue is wholly dry and sarcastic as you'd typically expect from something like the Mario & Luigi series. The music is fantastic, and the jazz motif is something you can groove to. This is one of those rare soundtracks where I found no song that just sounded out of place and stupid, or worse, childish (...Toad's Expedition theme from SMG, anyone?) So, having great music all around just brings the game a few notches higher for me.
Yes, this game, while borrowing elements from Mario RPG games of years past, of course, returns to Mushroom Kingdom basics, so think of it as a successor of sorts to the original Paper Mario. Keep in mind, this is a bite-sized RPG adventure; a "lite" Paper Mario, if you will. I clocked in at 19 hours and 19 minutes from start to finish while the usual benchmark for typical RPGs seems to be around 40 hours. You feel like you're getting deeper and deeper into the game then you suddenly realize that it's coming to a close.
There are some quirks: The sequential battle system that Kimimaru, for some reason, put spoiler tags around in his post is kind of screwy. Not being able to choose sort of affects the flow, and if you have the opportunity to use more than one sticker, it will make the order you attack the enemies in sequential (e.g. the battle sticker you have in the second slot will always attack the second enemy in line regardless of if your first sticker killed the first enemy in line or not. Same for third sticker/third enemy in line). Maybe the developers thought that assigning different stickers to different enemies during battle would be too confusing.
Thing Stickers, as much as they were shown off, were implemented weakly which sucks considering that was supposed to be the big thing about Sticker Star. There are points where a Thing sticker is necessary to advance and you have no idea which one you're supposed to use. If you use the wrong one during Paperization, well, sucks to be you because you will lose it. You also get no hints as to which ones are useful in boss battles or anything like that. Which brings me on to my final point...
Kersti (your Sticker partner or whoever) is the most useless freaking sidekick I've ever seen in a Mario RPG. She is the I AM ERROR of the Mario RPG world. She never has location-specific information on hand, ever. She also never has advice on puzzles, what Things might be useful, and no info about environments, where you are, or any hints on what you should be doing next if you're stuck. When you summon her she spits out some quip, and very rarely do you see an option to get more advice, which, more often than not, is incredibly generalized. I've gone through entire worlds where she says the same couple lines over and over and doesn't offer advice.
Besides these few flaws, I believe the game is deserving of the 8.3/10 IGN gave it. I'd go as far as to give it an 8.5. Just remember that it's almost like Mario 3D Land. Everyone coming off Mario Galaxy 2 was thinking, "MAN IT'S GONNA BE LIKE GALAXY 3DS," but while it was great, it couldn't quite live up to the same amount of awesomeness the Galaxy games brought us because they were limited by the 3DS' capabilities. So, if you can keep in mind, like I was saying, that it's a bite-sized, portable version of past Paper Mario games and look past its flaws, you'll have a lot of fun with this one.