I'm going to throw my .02 in as a huge fan of Harry Potter, and a "diehard" Disney fan, card-carrying member of DVC, and someone who has witnessed the progression of Universal over the years, albeit with very few visits.
I am very excited to see what Universal is doing for the Wizarding World. I know that Jo Rowling is very much involved, making sure her "world" is represented as best possible, so I'm not worried about Universal making a wreck of things.
But, my first visit to Universal was back in 1992, and I must say I was not terribly impressed with it. I thought many of the attractions had the same vibe. How many disasters can you see with King Kong and Earthquake? I had the same impression with those as Catastrophe Canyon at Disney-MGM (Hollywood) Studios. So I can honestly say my first visit did not impress me much.
Cut to 2000. Islands of Adventure was open, and there were a few changes to Universal overall. I went there mostly for IOA, and I was impressed with most of it. I thought Disney could have taken a giant cue from the Spiderman attraction. I thought that Universal outshone Disney with that. Granted, the other thrill rides around the park were basic, but I think Universal did a decent job theming them. I think they dropped the ball with the biggest waste of a beautiful exterior space (aka Poseidon's Fury), but I had a better impression of Universal from that trip.
Cut a few years later when Universal had three resorts onsite, added Men in Black and The Mummy. My friend got a great passholder rate, so I stayed with her for a couple nights at Portofino Bay. I have to say if I hadn't known it was smack dab in the Universal area, I would have thought this was a really first class resort. When I compare the amenities in the room (and the grounds), I think Portofino is better than many of the Disney deluxe resorts. And since there are only 3 hotels onsite, Universal could offer front-of-the-line access as a perk, something Disney cannot do because of the sheer volume of rooms on property. My opinion of Universal went up another notch.
Now, I haven't seen the new Simpsons ride that replaced Back To the Future, and the Wizarding World isn't open yet, but you can be sure I will make a trip out to Universal to see those. I don't tend to want to visit Universal much, but the new Wizarding World will be a major draw for me.