I had the chance to go with my brother a couple of years ago and we really enjoyed ourselves. Having also been to Miniatur Wunderland in Hamburg there are some similarities, but also some differences.
The modelling in both is top notch, with MWL being constructed by the team members/employees and Gulliver's Gate, from what I read on site, being largely subbed out. The team in Hamburg is quite large and very technical.
MWL is located in the Speicherstadt area on the harbor front, beautiful old warehouse buildings, but again not super prime or super expensive in comparison to Times Square.
The Braun brothers, the force behind MWL are master marketers and have a background in the club business. They understand entertainment. If you go into any train or hobby store in Germany you can buy a DVD or magazine about MWL. They really are the life force of MWL in my opinion.
Finally, model railroading and model making are just more widespread and appeciated in Germany. I read somewhere that one third of all German households had at least a small train layout 50 years ago. That number has come down, but there is still a love of trains deep in the society. Plus the brothers Braun knew that to have widespread appeal you just could not have a large train layout alone, but needed a true exhibit, a "Wunderland."
I think both are fantastic, but there are some major differences which I believe make one more financially successful than the other at this time.
Miketg