After playing with Danger Rooms for a bit, I have two suggestions for them:
1) Have a choice between Danger Rooms. I'm not saying give you all the room types and let you pick, but maybe a choice between Random Room A and Random Room B. Once you choose one you can lock the other. I find myself often losing 3 Energy because I run into the room and see it's a room I cannot tolerate (Like the one with 80% spikes. Yeah I know there's a strategy to it, but it's still an excessively hard solo in my opinion).
2) Give a preview of the monster you will encounter. Put maybe 2-3 of the monster you will fight in the room already, waiting for you, so you have an idea of what you're going to fight. I tend to solo a lot, and at Tier 3, soloing against Gremlins in a Danger Room is practically suicide. I absolutely hate when I hit a Danger Room, and if it were ANYTHING else, I wouldn't have a problem, but it's freaking Gremlins, and I get screwed over for it. You can't leave the Danger Room mid-fight if it's something like that, and I'm sure everyone has a monster they just hate (And probably will get more as the developers add more monsters). I think a preview to what the Danger Room will be before you hit it is a great idea to prevent people from raging over the DRs.
Having a choice between two rooms is pretty nice, but I don't quite like the idea of a preview for the danger rooms.
It's better to keep a bit more degree of surprise for it to be dangerous imo.