Some of the later levels took me about 40-50 tries to finish (compare with "That one level" below). But I tried to put the hardest spots at the beginning of a map, and from there it gradually gets easier most of the time. I remember super meat boy had a few levels that were not that hard but quite long - but the hard part came at the very end. This is something I didn't want and tried my best to avoid it.
In total i needed about 3 hours to play through everything (savegame time counter). Of course I have and will keep the save game with all the replays, in case anyone claims the maps were not doable in par time. (Which I forced myself to do without any bonus items or tricks, which would have made it considerably easier).
Now, without giving too many spoilers away, here's an annotated list of "tropes" that await a player:
Rule 50 - I fulfilled it by making this mod.
Platform Hell - Some of the gameplay resembles this. But not all. Only one of the maps is deliberately unfair - if you know the game it is based on you will instantly recognize it.
Jump Physics - Most levels require good mastering of these.
Nintendo Hard - It definitely is.
Mushroom Samba - The intro. 'nuff said.
Nightmare Fuel - Some of the later levels, and the final boss.
Everything Trying To Kill You - This is nothing new.
Malevolent Architecture - I built the maps, I'm responsible, I'm an evil bastard.
That One Level - You will love it.
Wall Jump - Absolutely required.
Everything's better with spinning - A new move: Spin in the air to finetune your jump direction slightly!
Bullet hell - Some of the late levels.
Macross missile massacre - Especially the last level.
Excuse plot - Ah well. Sort of.
Warp zone - 5 of them.
Double Jump - Comes in *very* handy once you found it.
Eternal engine - The desert + volcano levels.
Nitro boost - You will love it once you found it.
Advancing wall of doom - Some levels have this.
One hit-point wonder - But only because jumping into a huge sawblade isn't something anyone could do a second time. Note that not *everything* kills with one hit, that would be unfair. Entities in the later levels have their normal attack power, and Naija has 5 health, as usual.
Resurrective immortality - Otherwise it would be unplayable.
Death is a slap on the wrist - This directly adds to the above.
Mercy mode - Does not exist. No mercy.
Brutal bonus level - The warp zones.
Spikes of doom - As nice and shiny as sawblades! And, the last level, as well as 3 of the warp zones.
Sentry gun - Missile launchers.
Sequence breaking - Some levels are deliberately set up to allow this. If you find out how...
And because i like to randomly post this image, have it now:
