This pack is one of the hardest I think I have played in MC yet, it has some bugs but nothing game breaking. It is definitely one of those it's not if you will die but when.
Between all of the added mobs and difficulty level being one shot by a skeleton is a common thing in this pack. They have locational damage and the skeletons love to headshot you, almost like playing COD against them. lol
RLC hurt my brain due to the fact that I have played a couple of hours of it and continuously died over and over and over again and my refusal to play in a non-legit way hurts my brain severely.
Personally, I think RLcraft completely misses the point of Minecraft. It's unnecessarily hard, and it's bogus bullshit. If you want a completely new Minecraft experience with a big difficulty spike, I'd say try it out.