It was immensely satisfying to master this hold. As calamarain mentioned, the difficulty is just right. Nothing too simplistic, but after some struggle you'll still get it. In general, the secret rooms are very well hidden and they are fun to locate. Specifics:
Outer Defense:
1N3E is an awesome creative construction of one-way passages. 2E took me a long time to figure out how to maneuver from one entrance to the next. 1W is annoying. I hate orb puzzles. Yeah I know it can be back-traced, and you put an escape orb in the beginning, but I still hate orb puzzles...
Repository:
All nice rooms, especially 1N1E. I like bombs going off. 1E took some time, but it was fun to play with.
Flooded Repo:
Many straight less difficult and beautiful little rooms. 1N took awhile until I managed to take the speed potion. 1N1E and 2N2E are great mimic+gel puzzles where the finding where to stab first is hard, and the rest falls apart.
Briar Patch:
This is a fantastic level. I enjoyed all of the secret rooms, especially
Click here to view the secret text
×2N3E for the fun interaction between bombs and briar.
1S1E is easy in the sense that any wrong move results in Beethro's [literally] immediate death. 1S2E is a fun path-finding puzzle. 4E gave me major headaches to keep everybody alive. Likewise for 2E.
Halls of Variation:
Finding a sequence of popping blobs is not really my type. So I enjoy this a little less. Nevertheless I won't complain, I can't expect everything to be exactly as I like it. The 5 non-blob rooms are very fun though.
Inner Defense:
Talk about room reuse. Entering the room 10+ times for 10+ different puzzles.
Cheap Tricks:
Favourite cheap tricks: 1S and 1N. 1N is evil. What's the deal with 4W? I got stuck! Oh well, it's post-master, so I can let Beethro rot in the level.
Overall very enjoyable. 10 fun and 7 difficult.