My experience at Universal hasn't been "disappointing." In fact, we just went for the second year in a row. My point is that, for us, it's just not the same as WDW (outside of HP), which was the point of the OP. It's not as magical. Feels like most other theme parks you can go to outside of the Harry Potter lands, which are VERY well done (although lacking in rides).
You can absolutely have a good, even a great time at Universal. It's just not somewhere we want to spend days upon days, as opposed to WDW.
Not to mention the fact that Universal is literally right next to the freeway, whereas WDW has built a massive complex where you can feel completely encompassed during your whole stay.
Also, I beg to differ on the photo opportunities. I looked and looked and looked and looked for photographers around Universal like they are all around WDW. I didn't see them. You can find them at some of the character meet-and-greets (but not all) but that's about it. They're all over at WDW. I would have loved a professional shot of us in Diagon Alley, but had to settle for a worker using my iPhone. Just not the same.
Bottom line, Universal is a 1-day park for us, and a short day at that, even for both parks. We spend six times that amount of time at WDW.