My review of Sealtower:
This level...ugh, there's so much wrong with it, I don't really know where to begin.
Well, I guess I'll start at the beginning. In the first section, there's a tower not long after the start. First time players will think that this is where they're supposed to go, but no, the player actually has to go
past the first tower and get an ax in another tower later in the section in order to go through the first tower. If the player climbs the first tower without getting the ax in the second tower, he/she won't be able to progress past some blocks. When I first got to the blockade, I thought that I had to collect all of the coins in the tower to progress (since I didn't know about the second tower at the time), but I soon found out that that was a waste of time. After the blockade is removed and the player passes the first tower, the path splits in two, and this is where the level's biggest flaw (aside from
maybe its length) makes itself clear: the level is way too cramped way too often:
It's a shame, too, because other than all of the cramped corridors, your NPC placement wasn't too bad.
Another annoying part of the level would be here:
The blocks in the screenshot are invisible at first, and the pipes only lead down, not up. In other words, you force the player to backtrack through this section
twice before being able to proceed, and making the player go though literally the exact same obstacles multiple times is something you should avoid doing.

This is the part of the level (before the midway point) that caused me to give up and start cheating:
Okay, so the entire point of this tower is to climb up here, stomp one of the Koopas that gets generated from the pipe on the left, then go back to an earlier part of the section to break a wall...
However, if the player activates both of these invisible blocks, which all first-time players will do, there is absolutely no way to get out of this part of the section, rendering the level unbeatable and forcing the player to kill himself/herself, and yes, I looked in the editor to make absolutely sure that I wasn't missing anything.

Now, on to the second tower in this split path:
I am yet to find a pipe maze that isn't incredibly tedious and boring; yours is no exception.

Now, this tower also has its own split path, but the problem is if you go to the right first (where the pipe maze is), you'll fall past these invisible blocks and end up on the second floor. If you go left, you'll end up on the second floor no matter what, so if you go right first, you'll have to go through the pipe maze again, which is extremely annoying.

Once the player gets the axes in both of these towers, he/she can go inside the top-center tower in the fourth section, where the music finally changes. Oh, that reminds me: throughout the majority of the level, Watchtowers of the Seal is playing; that may not seem like a big deal, but the song is only 48 seconds long! Remember how, in the first post, it is mentioned that this is a long level? That is an understatement. If you're going to make a level this long, the least you could do is use a song that isn't this short.
Anyway, inside the top-center tower is an SMB1 Bowser that the player has to fight with shells. Now, on top of being a pre-programmed AI in an empty room with a generator that you have to use as your weapon (which is its own category of bad level design), once the first SMB1 Bowser is killed, the player has to fight a second one, which just adds to the annoyance factor. After both SMB1 Bowsers are defeated, the player
FINALLY gets the checkpoint. That means that if the player dies
ONCE during anything listed above, he/she has to go through all of it again, listening to Watchtowers of the Seal (seriously, I got sick of the song by this point). When I got the checkpoint, I turned off God Mode since I thought that, maybe, the level would get better.
Anyway, after the checkpoint, the player has to go back to Section 4, jump down, then climb to the center of the center tower to proceed. That part is moderately annoying since the player still has to go through a section traversed countless times before, and it would be better if the door by the midpoint went straight to Section 9. Oh, and Watchtowers of the Seal begins playing again.
So after Section 9, the path splits once again, but not before the player comes across this obstacle:
The enemies are generated too quickly for the player to be able to run past one without getting hit by the next one, and the only way to get past is to jump on one under the ? blocks, which can be annoying since these enemies bounce.

For the tower on the left, the player can see the ? block before the Podobos are spawned, and first-time players will hold left to go to the ? block and end up getting hit by the Podobo. I recommend removing the pipe so that the player can see that there are Podobos there without taking a hit.

Remembering what happened with the Podobos, I decided to stay still when I fell to this part, and ended up falling into the lava and dying.

That's another major problem with your level: all of the blind jumps. The player has no way of knowing whether or not he/she is about to fall into lava until after he/she has been killed by it, and your coin placements aren't enough of an indication. It was around here that I activated God Mode because I was getting tired of this level's blind jumps and your song choice.

By the way, the above screenshot is from the second tower in the post-midpoint split path. Like one of the towers before it, this also has a split path, and this one also isn't beneficial. You see, once the player makes it here, he/she can either go left or right. One path leads back to the beginning of the section, and the other path leads to the necessary ax.

If the player goes left, not only does he/she encounter the blind jump I commented on above, but he/she will also be sent back to the beginning of the section! There's no indication which path leads where, so it's a total guessing game for the player and a bad design choice for the level's creator.

If the player goes right, he/she will come across this part. First-time players probably won't think that they're supposed to just jump up the platform, but spin-jump on the Podobo instead. However, that just gets the player killed.

Further along that path, the player will encounter this off-center Piranha Plant:

You should really do something about it, since the player can spin-jump on Piranha Plants' spawn points:

So, what happens once the player gets the ax? He/she is sent back to the split path, of course!

To avoid confusion for this tower, I recommend blocking off the left path from the main path, then have the door by the ax warp to the left path.
After all of that, the player
finally makes it to the boss of the level, and what is it? An SMB3 Bowser in an empty room with a generator that you have to use as your weapon. Not only is it boring, but the boss can be broken if the player just stays above one of the generator pipes, making it one of the easiest bosses ever:
By the way, do you know that SMB3 Bowsers take TWENTY HITS to be killed by projectiles? It is rarely, if ever, fun to fight SMB3 Bowsers with projectiles, and I've never encountered one that is fun. This fight is no exception, and since it can be broken as shown above, the fight is just extremely boring.
In conclusion
The level is too long, the song choice is too short, there is too much waiting and too many blind jumps, and the bosses are just pre-programmed AIs in an empty room with a weapon generator. There are a few areas that don't have anything wrong with them, but they are so few and far between, it hardly makes any difference. I'd say this deserves a 3/10.