We're long-time BWV owners and WDW veterans, and we made our first trip to Universal Orlando last June and enjoyed it very much. We stayed 4 nights at the Royal Pacific Resort followed by a 5-day Disney Dream cruise.
One word of caution re: previous posts reporting short waits for attractions, including for Forbidden Journey which is the signature attraction in the Wizarding World of Harry Potter section of Islands of Adventure. You will find very long waits during busier times of the year so please keep this in mind if you're day tripping from WDW. Universal resort guests are allowed early entry to IoW specifically for WWoHP and the crowds become overwhelming very early. By midday, there is a long wait simply to enter WWoHP because it is a relatively small 'land' and then you could wait a couple hours to ride FJ.
This is not to dissuade anyone from day tripping to Universal. Quite the opposite -- just be prepared for large crowds during busier times of year and plan accordingly. Also, keep in mind that WWoHP is just one of several 'lands' in Islands of Adventure. The park has a large number of world-class attractions, and then the Universal Studios park has even more. If your only objective is to experience WWoHP, you'll still pay for a full-day ticket to IoA so go early and experience the entire park. Better yet, do what others are suggesting and stay at least one night at one of the Universal resort hotels which will give you 2 days of Express Pass priveleges (similar to Disney FP but unlimited for virtually all attractions).