I don't like the way the river is always 5 tiles wide. It looks boring and artificial... None of the streams I've seen are like that. Make some bays in it, maybe even an island somewhere and some variation in it's thickness, so that crossing it is harder if the PC is too stupid.
I'm not sure how exactly should the river be shaped. This simple shape looks good enough for me, it's just a short part of an undergorund river, after all, no large meanders attached. But I could change it, of course, if you didn't like it that much.
or a more constructive criticism: I like the idea of making enner harder, but make the river appearance a random chance. come up with 3 or 4 twist on enners level with the twist randomized each game. I think if all you do is add a river, its going to take a short period of time for people to figure it out how to deal with and it reduced to a mere speed bump.
Maybe instead of a river you could have a random level effect that makes killing him harder. what are the main tools for killing him : tele/telecontrol ,esp, detect material, wands. Take a random one away each game on his level, so you don't know what you are dealing with until you get there. "you feel your teleportation being blocked" "the screams of the enner keep you from concentraing on your scroll, it is wasted" "the wailing of the foul beast prevent you from honing your ESP" "the sonic waves disrupt the wands magic"
something like that make one or two of them randomly in effect for the level - it will cause players to have to come up with multiple strategies for dealing with enner instead of having one playbook to breeze though like it is now.
Having a level generator select from several potential layouts would be cool, but impossible with the current generator, I think, so some change to the code would be needed - not my cup of tea.
Anyway, if that's ever implemented, we would need much more special rooms, and every game there should be only several of them placed, so that you don't always eventually run into the orc room.
Also, it would be nice if e.g. the zombie level could be randomly swapped with the mine-finder level (I've read that level idea in some ideas collection), so you would have 50% chance of having zombies and 50% of huge minefield.
I don't like the idea of forcing any playstyles upon the player (eg. get the belt of levitation or find a method of controlled teleportation). And giving the player handouts like guaranteed blink dogs or wands isn't really IVAN's style. I think there should just be a bridge across the river so that anyone can cross it; it should serve more as scenery than a major obstacle.
What if we had a bridge in the middle of the river, with the enner always on it?
The room could be placed semi-randomly on the level, so you would never know how near will it be to the upstairs, and tunnels are completely random, so no easy path every game. That way, you would be always able to cross it, no items required, and the river would be something like a boss arena rather than outright obstacle.
I must say I still like the idea of isolated stairs, but too many voices have spoken against.