I agree that no-map doesn't really change the difficulty... until you get to Mistlands, assuming you're also playing no-portal. You can get lost extremely easily, and, besides the obvious issues of having to scramble for a place to sleep at night, you can also get into situations when you're food is running out and/or your weapons and armor are breaking. Not to mention the difficulty in acquiring wood.

I think no-portal makes even more of a difference, for all of the reasons listed above, but also having to potentially run across dangerous territory multiple times, rather than taking the express flight. Not to mention just being able to go to your main base at night to restock and reload, and being able hop in your portal at the first sign of danger to do the same.

For me, though, I don't think any real difficulty increase is very meaningful unless you're playing permadeath. I played permadeath until ML came out, and stopped because I thought it would be difficult to get all the way to ML without dyeing once, and I was probably right.

I think I'm about ready to switch back to playing PD because, any time I get into a difficult situation, or contemplate something challenging, I always have it in the back of my mind that it really doesn't matter, since I'll just respawn and have to work through getting my stuff back (or not).

For me, without PD, nothing really seems like a challenge. Take on a 2* soldier with knives and Fenris armor? Sure! It's not like it's going to be game-over.