Super Mario 3D Land - World 8 is when the game stops being snore worthy. Pretty good right now.
I got all of the golden flags and star coins for the first six worlds. The thing that bugs me the most about that game is that you pretty much only need the Tanooki suit. The other powerups seem like novelties. You definitely need the Tanooki suit to get the golden flags with relative ease. Also the diorama feel of the game resulted in several cheap deaths for me. Fortunately they don't skimp on the 1up collecting opportunities.
Update: Got all star coins and all golden flags up through the 2nd Special World except for the very last star coin at the last stage of the regular game. For some reason I can never time the jump between the fireballs while keeping on the ride. It's been killing me, I even got the white and gold tanooki suit of shame 
The special worlds are a bit better but I wouldn't say they were Galaxy quality. It just reminds me of another take of the Sunshine side levels. Still a damn fine game though.
Edit: I'm going through Special World 4 and holy fuck, this game is starting to bite back. Hard. Still have about 190 lives. At this point, I can hardly get anywhere unless I'm Tanooki Suit Luigi.
Finished Special World 8 except for the final stage, which you need to five star the game to unlock. According to the activity log, I logged in 10 hours and 30 minutes. I do intend to five star the game - I need to get all of the golden flags, which there are a few left I need to snag. So the overall length is probably like 11-12 hours. Hopefully I can get the game wrapped up in its entirety tomorrow.
Overall I really liked this game. I'd almost consider it a classic and something I can see myself replaying again some day. The special worlds get pretty nuts after a while. You always got to keep moving, even with Shadow Mario/Luigi on your ass while fighting against a 30 second time limit. Almost all of the stages in the last couple of worlds had at least one of those attributes. However, everything is tough but ultimately doable and the levels are designed well enough to where if you screw up, it is pretty easy to figure out how to get past the obstacle/enemy/whatever. There is some trial and error involved but some stages I completed by sheer dumb luck it seemed. Also I finished the game with 455 lives

The next 3DS game I'm probably going to play is Samurai Warriors.