Pros
You get to meet tons of people at Gensler in New York City. There were 40+ interns when I was there, and you make fast friends with these people. You get to spend each Friday working with all the other interns on an intern project, that is presented at the end of the summer. The work is diverse and fast paced, which is great if you're an ambitious rising architect. I did have to stay late a few nights, but you get paid 1.5x for overtime hours, and you get dinner paid for and cab ride home if you stay super late. They take care of you here.
Cons
Very few, other than a few late nights I had, but the late nights depend on your project manager and the project you're working on. I also would've liked more than $15 / hour in NYC...maybe $20 / hour is more reasonable.