Ruin Explorer
Legend
I dunno. It doesn't fill me with hope for the encounter building guides being as good as 4th's. 3e's CR was garbage, and I'm really hoping 5th isn't going back to that where CR2 = challenge for 4 level 2 characters. Someone mentioned somewhere, here or Reddit, that 5th's CR is more of a threshold, like "don't use this if the party level is below this number" which I guess would temper that lethality.
This is something I'm concerned about too.
4E's encounter building was wonderful. It meant that I didn't have to think about whether this monster was going to randomly wipe the floor with the PCs, to analyze it's abilities to see what might suddenly blow up and so on. It really was a very reliable guide (especially post MM3-math) to how hard an encounter would be for them.
3E's CR was actively detrimental to my judgement. In 2E I could stare at a monster and have a good idea of how dangerous it might be, and whilst that took time and was annoying, and sometimes ended in fudging, it was only moderately bad. 3E, though, I had to do everything I did in 2E, but I also had to slowly train myself to ignore the CRs which the game insisted worked, because they were desperately misleading. A monster that could easily wipe out a party of equal level might have the same CR as one which was barely a challenge.
I'm sure 5E will beat 3E on this one, but I really hope they come somewhere near 4E, too, as it was a tremendous asset to me as a DM, reducing prep time, encouraging me to use monsters unfamiliar to me, and having a reliable idea of the effect of an encounter on the PCs, which allowed for better adventure planning and so on. If you're right and they also act as "You must be at least this tall..."-type measurements, great.