The Spawn Building
I enjoyed this rev's spawn compared to the spawns of past revs. It was easy for players to exit if they wanted to get out immediately, but had plenty of goodies at hand for those looking for them. I also really liked the spawn museum on the 2nd floor to take a look back at nerd.nu's history. The amendments made to spawn were also beneficial.
The Overworld Map
I was initially hoping to have a smaller map for this rev, but now I think 9k x 9k is a good map size. This map size will definitely be good for next rev when people will be hoping for large oceans to explore. I don't know if it's possible, but would there be a way to use the current version of OTG/Biome Bundle for terrain generation on land while having 1.13 vanilla oceans?
I know we'll have plenty of oceans next rev due to 1.13, but i would recommend not having an ocean right next to spawn, or at least not have spawn surrounded on three sides by ocean like in rev 18. That seemed to hurt that rev's infrastructure quite a bit.
The main biome that is lacking this rev is desert - more specifically, deserts that have more than one or two layers of sand before hitting sandstone. I know that some deserts were added to the nether specifically for sand collection, but i was afraid of ruining all those beautiful landscapes! Last rev, there were some giant sand worms that were left all chopped up and floating in the air because someone had taken all the sand there ;_;
Other than that, resource distribution was good!
The Nether Map
I like having custom nether maps and mobs! I don't know if the Padmins are still working on it, but it would be nice for the custom mobs to have named drops for their armor and weapons (besides the pixie stick, or whatever it's called).
The End
I would like to see tougher Ender Dragon fights continue, but having every hit spawn more mobs is tough on people who don't have great computers (I personally didn't have problems, but I know plenty of other people have).
Mapworld
The only WorldEdit commands I can think of that may be useful are //cyl and //hcyl so it's easier to make circles.
Portals
The method that was used to release portals was good, as well as having little puzzles to solve to find the last 6 portals. I think it's also a good idea to have an irregular portal distribution like we had this rev so that people can't just guess the general area of where a portal would be.
Iron Golem Spawners
No complaints or concerns here!
Custom Spawners
All the custom spawners we have right now are good. We shouldn't put any in the nether though, especially if we're going to keep custom mobs.
Custom Drops from Ore (Fossils and Rares)
The custom drops were a great addition and I hope they come back next rev to match whatever the theme is!
Custom Saddles
I like having the saddles as both prizes and trades.
Elytra
I think the method of obtaining elytra was good this rev. While I generally don't use them until the second half of the rev, I don't think it would be a good idea to gate people off from getting them early on if they want them.
While elytra (specifically powered elytra) has hindered roads and rails a little bit, I still see players creating them, mainly at the beginning of the rev before getting elytra. I think we've done a good job of helping infrastructure with the addition of a spawn rail station the past few revs.
Events
Types of quests I'd like to see return:
The Knight's Quests from rev 21- there was a wide variety of challenges to take on (scavenger hunts, trivia, redstone puzzles, etc).
NITWITS from rev 20 - I liked this sort of scavenger hunt more than other ones since it required you to think a little bit and also encourage people to work together to solve the puzzles. It's better than hunts like the Lost Slime Golems which are just "Go find these things. Where are they? Somewhere."
The Viridian Journals from rev 17 - I thought this was a cool idea to add a little lore to the world.