Oh, man, this is fantastic stuff! And no-one told me about it until yesterday. (I've been too busy with SttD and other things to look at Architecture much, but I'm glad Blondbeard did tell me.)
I've only played up to the start of The deeper tunnel, and peeked ahead a little. Comments so far:
× One general thing: If it looks like you could exit a room somewhere, you should be able to do so. In a room such as The rebel nest:4N for instance, a player who doesn't have editing rights, and therefore doesn't know that there is nothing on either side, is going to try exiting the room all along the sides, just to make sure, and feel disappointed and maybe annoyed. Better to put walls along the sides.
The rebel nest:
Ent: Not the best room in the hold, but ok. One thing, if someone tries the hold, they see an easy room, then this. If they get stuck here, they don't see anything else. I don't really see how myself, but ideally if the rest of the level could be accessible without having to conquer this room.
Bomb mazes: Very nice. In 1N1E I don't see the point of one of the orbs by the entrance. Not as if it's difficult to avoid hitting it, and a wall there would force hitting the other one just as effectively.
Fighting arenas: Not really my kind of room. Not too hard if you take it slow and careful. Another checkpoint in 4N won't hurt.
1E, 1S: Excellent rooms. In 1E I had a spawn cycle to spare for the NE mother, which strikes me as unintended.
1N: Difficult, but interesting.
2E: I don't see what the bombs and the two little doors by them are about. I just cleared the room without worrying about that. I could have hit the orbs or not. It didn't matter. Well, I can see how it might be used, but that looks much more difficult. If it's a red herring, it didn't work.
3N: One of only two rooms in the hold that I really don't like. Most people don't like orb puzzles. I hate them. (Orb puzzles, I mean. I have nothing against people who don't like them either.) Good thing the two rooms behind it are secret and very simple, so I can ignore this room.
Goblin chase:
Ent, 1W, 2W, 4W, 7W: Much easier than some of the previous rooms, but fun. 7W is a bit more difficult.
3W: Brrrrrrilliant herding-goblin-through-maze type room. Best one I've seen.
5W: Nice timing puzzle.
6W: Urgh.. Not my favourite room.
The civilisation:
Ent, 1S: Ok, I guess. Should perhaps be tighter at this stage. I had about 20 moves to spare in each on my first attempts. The much earlier Rebel nest 1N was a far more difficult timed room.
1N: Fine.
5N1E, 5N4W: I'm generally not into Slayer hordes, but these two are actually very good.
5N2W, 5N3W: Easy.
The tunnel:
Best level so far. Excellent theme development. There's a little leeway in all rooms (I have between 1 and 4 moves to spare in all), which I like. I'm finding 1W a lot more difficult than the others (except 7W, which I'll get back to). You may want to consider moving it to the W. I also found 3W more difficult than 5W.
6W: mmmmm...Like The deeper tunnel 2N1W, there's nothing difficult about these snake hordes. This one's much easier than the rest of the level. TDT 2N1W is a little tedious.
I also noticed a couple of typos etc. I'll post a list when I've checked everything.
Great work, Rheb.
Most of the others are 
This is all Rasmus creation.