This level is actually quite well made; it has a variety of NPCs (although the Boom Boom is just random and the Chucks move too fast to react to), and it even has a bit of variation with block placement while still retaining the feeling of being on a train. However, the background object and block sprite-swap that are supposed to be part of the front of the train are clearly two pixels above the main train graphic. To fix this, uncheck Auto-Align (it's to the right of the "Water" box) and reposition the two graphics so they connect with the NPC sprite swap. Another problem with the level is that, on the second train, there are invisible blocks beside the 1-up. I know you put the blocks there to prevent the player from getting the 1-up from the left instead of going under and getting it from the right, but the problem is that the blocks are invisible, meaning the player won't know they're there until after running into them, and that's unintuitive. They should be replaced with visible blocks, like block-1. Speaking of invisible things, why are the Lakitus invisible? It's not like you made it so they can't be killed, or that they don't harm the player; plus, it looks awkward having Spinys spawned from nothing. It would be better if you just left them as Lakitus. Also, while the transition into the tunnel was done well, the transition out of the tunnel (shown in your fourth screenshot) just looks random and amateurish. It would be better if you flipped background-11 and had it replace another background object, like background-54 (while that background isn't as wide as background-11, you could simply remove the half of the image that's pure black so that it fits in the smaller dimensions) so that both of the transitions are similar.
There are also a couple of unfairly-placed Bullet Bill generators (keep in mind that the level autoscrolls, so if the player waits too long, he/she gets crushed by the edge of the screen):
The first unfair generator is on the far-right of the screenshot (the editor-hand is pointing at it). Once the Bullet Bill Cannon staircase fires, there's not enough time for the player to get to the top before the generator in question has fired a Bullet Bill. By the time the player has reached the top, the Bullet Bill is right below the generator just beside the staircase, and at that same time, that very generator shoots another Bullet Bill, and the combination of both of these Bullet Bills makes it unnecessarily difficult to avoid getting hit. I recommend moving the far-right generator further to the right by a couple units.

The second unfair generator is the one near the top-right of this screenshot. Similar to the previous circumstance, the player will be standing on the leftmost generator when the one directly beside it (just on the other side of the doughnut blocks) fires, and when it does fire, there's not enough time for the player to make it on top of it before a Bullet Bill from the unfair generator is also on top of it, giving the player very little room (and time) to dodge. I recommend moving this generator a couple units to the right as well.

Also, no matter how you position them, these background images overlap each other in undesirable ways:
It would be better if you used the editor hand to put the windows over the bricks, prt sc and paste the result in a PNG or BMP, use an online converter to convert the image to GIF, and have the result sprite-swap the background2 image. That way, you wouldn't have to worry about this overlap.

Lastly, the boss is just lazy. It's just a stationary Mother Brain sprite-swap and a few Rinka generators. If you're going to have a boss, at least try to put forth the effort to make something unique; if you won't do that, it's best to just use a normal level-ending NPC like the SMB3 Roulette or SMW Goal Tape.
Summary:
GOOD:
-Graphics aren't terrible.
-Music fits the level well.
-Block placement is okay.
-NPC placement is done well.
BAD:
-Floaty train graphics.
-Chucks move too fast.
-Unnecessary invisible blocks.
-Unnecessary invisible Lakitus.
-Amateurish transition.
-Unfair generator positions.
--LAZY BOSS FIGHT.
In conclusion: While the level does have a couple of relatively big problems, it's still quite enjoyable overall. I'd say this deserves a 6/10.