I find that most of the time you can deduce some level of information to make an educated 'safe' guess. I'd say part of the game is managing 'safe' exploration to find the bonus items like chests, heals, etc. I will say that there is a tendency for the start of a dungeon to be the most RNG prone, where a bad generation could cause you to have limited options which halts progress sooner.
Yes, the large level (where you scroll) is the final level of the rogue-like. I was considering adding more but I felt like item builds were getting so good by that point that making more levels would be counter-productive to their difficulty curve. Instead, I opted to create challenges, and specifically the DungeonSweeper+++ set of challenges to amp up the difficulty/gameplay.