I’m another Phantom of the Opera fan with Les Miserables in at a close second (my dad and I are always debating over whether Les Mis is better than Miss Saigon, which is his favourite. I love both but Les Mis has the edge for me). As for the older musicals, Show Boat and Fiddler on the Roof are my favourites.
My dad once saw a musical production of Flowers For Algernon with Michael Crawford in the main role. I would have loved to see that, he said it was stunning and although it wasn’t a massive production, remembers it very fondly. The book was beautiful in my opinion.