Mid-town was great. People working there were very pleasant and helpful. And for New York City, it was pretty quiet surprisingly (although they do have ear plugs if you want them).
Test overall was a little different than GMAT Prep -- I think the GMAT Prep test are the best of anything out there on the difficulty of the questions (although
Manhattan GMAT does a pretty great job as well). For math, the questions were much different actually -- they required more thinking, and less calculating. Verbal was actually a bit easier than I'd seen before. Overall, get used to GMAT prep, and you should be fine.
on that note, I ended up retaking both GMAT Prep tests, and although my new scores weren't that much higher or different, I did end up getting a bunch of different questions. I didn't do the reinstall or what have you -- just clicked start, and got pretty much a new set of questions.