I have to agree with TomPhanto's assessment here. The architecture here doesn't quite feel natural, and the sprite-only crystals are a little too conveniently placed (that is to say, there's a lot of single, isolated ones at the edge of platforms that feel as though they were placed solely for the purpose of preventing enemies from falling off, with no real effort placed into making them "fit" into their environment). What's more, the challenge seems to come mainly from supersaturation of super enemies rather than careful sprite placement as such. This is where your slowdown is coming from, incidentally--all those red Elites tossing fireballs every which way is sure to cause a lot of that.
The biggest issue, though, is that this level demands too many contradictory things from player all at once. On the one hand, you demand speed--there is essentially nowhere for the player to stop to catch their breath, as if they slow down, they're going to get slaughtered. On the other hand, you demand accuracy--there's lots of tricky jumps, platforms that fall, and fireballs and blue Elites flying every which way, and any mistake means death, since the only powerups in the stage are so risky to get that they're simply not worth it (you actually made the first one far, far harder to get than it was in the previous version). On the mutant third hand, you also use enemies which provide a high element of randomness, preventing the player from even learning how to strategize around obstacles. The result is a level which feels like an unrelenting barrage above all else; more shell shock than depression. You seem to be aiming for an "after the devastation" effect, but what we get instead far more strongly suggests and active war zone. And that's a little too frenetic for depression, no?
That said, there is a potentially workable concept beneath all this. To wit:
I must say, I found this beginning screen quite striking. Now, the execution could use some refining--the crystal shield is a little too square, and the blue Elite can actually bypass it by flying up through the ground at the bottom--but as a concept, it's quite powerful. We have Mario huddling in the ruins of a house with a hostile party besieging this pitiful last refuge of his. This screen, I imagine, summarizes the mood you're aiming for here--Mario is alone and adrift in a barren, desolate landscape, bereft of hope and comfort, and the only other people around are hostile gangs of marauding Koopas. Fair enough--that concept can very much work here. However, you really need to play up the idea of being alone and adrift in a barren, desolate landscape, and play down the gangs of marauding Koopas. The problem is that this assault doesn't simply cast Mario out of his haven into an uncaring world--it just keeps pounding at him an never stops, giving him no time to reflect on his change of fortunes. The Elites are still perfectly usable in this stage, but their numbers need to be severely culled. A little of the Elites goes a loooong way--they're called Elites for a reason, after all.
One possible take on this (and this is, of course, only one
of the possible approaches you could take here) might be something like the classic journey through a post-apocalyptic wilderness, i.e. "Mario encounters few living beings in this ravaged wasteland, and those few he encounters are hostile". Sprites should thus be much fewer and sparser, and perhaps could lean more toward inanimate objects (e.g. rocks, hopping flames) or scavenging and vermin-type animals (e.g. Swoopers). Occasionally, a Koopa gang (including an Elite or two) may jump out of the shadows and attack Mario, but these should be more isolated skirmishes, and generally ones where Mario can either fight back or run away to quickly end the confrontation--whereupon he returns to the dreary wilderness, barren as it was before. This would better give the impression of a Mario stripped of all defenses and comforts, alone and exposed to an uncaring world. It still has the element of danger, but it's more the sort of blanket dread and the sense of having no one to turn to, rather than a constant "Ahhhh, I am forever in fear for my life on account of things flying at me RIGHT NOW!"
A few more points:
- Please, cut down on the Munchers. One of the jokes about the first SMWCP was that every single level seemed to feel the need to throw Munchers in, one way or another. We have lots of lovely mono-directional spikes for you in the ROM, and again, Alessio made some lovely graphics for them which match with the 13B tileset, and you are quite free to use these in your level. Even then, however, scattering hurt blocks about the level willy-nilly is generally not the best approach to a level--it's a bit of a cheap fallback.
- Be kinder with the powerups. The first powerup in the stage should not be obscenely difficult to get, especially if the stage is a particularly perilous one. And the more dangerous a stage is, the more powerups it should have--with a certain number of "essentials" being comparatively easy to get. Every mistake should not be player's last.
- Finally, remember that this is a more downbeat phase (indeed, it is the most downbeat of all the phases). It shouldn't be super-active--that's more the realm of Happiness and Anger. Obstacles should be a little slower here, a little less panic-inducing. They should still be tricky--but they player should have more time to think them over.
Again, there's a workable idea at the core of this, but needs a huge amount of refining before it can shine. Just because this is the endgame doesn't mean you need to overwhelm the player--in fact, that's the exact opposite of the approach you need here. Sometimes, less is indeed more--and sometimes, one well-placed sprite can fill in for three just strewn about.