I hope nothing has been done to tone down the difficulty level of the original. I bought it when I was a teenager in the 80s, and enjoyed reading it - but was never sure how it would play - and I wasn't a good enough DM to do it properly.
I actually had two modes in which I ran it: Normal and with full disclaimers.
I think I ran it normal, three times for three different groups. All with existing characters in an ongoing campaign. It was tough, but reasonable. Two of the parties made it out without loss. The third (middle, actually) was my only real-world TPK and included the previously mentioned wand of wonder. All three were a ton of fun.
At some point, someone wanted to play actual horror. So, I started running Ravenloft as a challenge to folks to see how far they could make it. The terms were that I never broke any game rules and Strahd had to work within the information reasonably available to him -- but the module gave plenty of excuses for Strahd to learn almost anything about the PCs. No one walked in blind. All characters were made for the module and not expected to survive. At some point, one PC actually switched sides and stayed as a permanent NPC (who was eventually killed), with the conceit that each run of the module was Strahd being cursed to relive the death of another incarnation of Tatyana/Irena and hoping each group of adventurers would finally bring the artifact he needed with them. Several other permanent changes were made, over the years, but none particularly important -- mostly tributes to the fallen.
When the 2E version was released, I upped the ante and started using all the rules in the various Van Richten's guides. I also kept allowing higher level characters. The last time I ran the module was in the early to mid-1990s and the party was, IIRC, six characters of sufficient XP that at least one of them was 25th level. That
may have been the poor paladin who was (player and character) completely cocksure that he'd be the one to defeat Strahd to the point of letting his guard down too many times and, ultimately allowing himself to be isolated by Strahd while believing he had the upper hand.
Wow. I just realized that module was my training ground for almost every dirty trick I've learned as a GM. It was a magnificent exercise in manipulating and misdirecting people for entertainment. I don't really feel bad about it because every group that played through had a blast and people kept seeking me out, during college, to be part of the next run through. I probably did the "horror mode" 10-12 times and probably would have done more, if we hadn't switched to WoD and Champions.