I'm currently DMing a Curse of Strahd campaign (slightly modified to fit into an existing world I am slowly building (following core rule books for the most part). I am however following the setup/plot within the actual setting exactly. All encounters are done exactly as-is.
One thing I have noticed is that the challenge ratings seem very high for certain encounters. Sometimes massively so. Here are some examples we have come across so far.
While completing the introductory section, "Death House" they were suspicious of the pile of refuse in the corner and attacked it to be sure. It then attacked them back. They were a party of four level 2's at this point - fighting a CR5 monster, Shambling Mound). They survived by sheer luck since I rolled poorly on attack rolls.
There is also an example from later in the story...
While making their way through "Old BoneGrinder", they encountered the hags in the upper two floors. They refused to leave so the mother called her two daughters to help her and attacked the adventurers. At this point the party was level 3, fighting against 3 CR 5s (Hag Coven, Night Hags).
It should also be noted that...
The series of events literally led them straight here after the fortune reading to find an artifact. They did gain two levels after defeating the hags and securing the sword. There was not much room for exploring, they simply followed the road and noted that this was one of the places they were recommended to visit.
It should also be noted - I gave them as much warning as possible prior to the encounters, noting the ominous feelings, and a number of other things to give them every chance. And in fact - both encounters gave them the opportunity to back out prior to the combat, and the option to run away when they realized how hard the fights would be.
Now, I realize there was some obvious deficiencies on these monsters that make them slightly easier in general - for instance the first boss fight, they could have easily kited him around the room and never given it the chance to attack (his movement was only 20ft per round). The second fight, the majority of their spells are not terribly bad, and can be resisted if lucky.
Am I missing something here - or is this the proper sequence? Should my party have been doing these encounters or should they have run away? I should note, although the first encounter seemed easy, the second had them all nearly dead (and frankly, had I been trying to, could have easily killed them all).