^^^Very true.
And like you, I went into Gentleman's Guide with little or no knowledge of the show. A friend and I were planning a trip to NY last summer and it wasn't so much on our itinerary. When it won the Tony though our interest somewhat peaked. We decided to see it (even though I still wasn't thinking I'd get into it). Turns out I really liked it a lot.
When I saw Les Miserables back in the late 80s, I wasn't sure I'd dig that either. Thought I might be bored with it. Turns out, like so many, I liked it a lot.
Conversely though, another friend and I were talking about Urinetown last week at dinner and it got me thinking of shows that I had heard great things about prior to seeing them, but then found myself not so enthralled by the show. Urinetown was one of those shows that just didn't resonate. My friends and I actually left at intermission. Just not into it, even though I had heard great things about it.
At any rate, the purpose of this thread was not to focus on negativity as one poster suggested. It was simply to see which shows didn't live up to your expectations, and which exceeded them. Which is why I added that second part of the question, so as to not focus only on the negative critiques.
Not that I consider this a thread of negativity anyway. Simply more critiquing of shows. Nothing wrong with that.
After all the professional critics aren't always positive, so it only follows that a board like this isn't always going to be roses and sunshine. 
Thanks for the responses, all.