As an original SMB1 fan, I've got some scathing remarks to dish out... with your name on it!
Great job using the SMB1 sprites; I liked the old-school feel. The main thing which gashed it for me is that the resolution is just too high. I guess it had to be done for the Tetris blocks to be dropped, but the res could still have been reduced by at least a third. More of this to come under Mechanics.
Overworld theme, castle theme and standard Tetris theme. Alright, good choice. I wasn't sure about the castle theme being used for the bit where you had to build your castle from scratch -- I kinda felt it overdramatised the whole thing.
This, I'm afraid, is where I have the most complaints.
The autoscrolling makes it very reminiscent of a SMB Lost Levels stage, but I don't know if it helped with exploration at all. You may as well have put in a time limit -- it would have served the same purpose.
That you didn't have a time limit, and that you put in so many blocks and areas to explore, means that I as the player ought to have been given the *freedom* to explore this! Autoscrolling really took it away from me.
Also, only World 1-1 was playable here.... but it was too darn long. I spent most of my time standing still and moving Tetris blocks. SMB and SMB Lost Levels, by contrast, are slightly more fast-paced. I feel like I've been severely handicapped, playing a slow and drawn-out level.
Now, moving on to coins, power-ups and power blocks.
1) You would normally expect, in an SMB level, to have coins strewn all about the place, not necessarily in coin blocks. There were absolutely none in this game.
2) The only possible power-up was the Super Mushroom. No Fire Flower? No Invincibility Star?
3) A lot of the ? Blocks were found in Tetris pieces, and were impossible to access. It doesn't feel like World 1-1 when you can only get 7 coins in the entire stage.
tl;dr: I liked the whole crossover idea, but it could have used a lot more thought. Resolution was too high, mechanics were not thought out, and it felt slow and drawn-out.