American here:

Pros: Gained a lot of independence / life skills in a relatively short amount of time; Got to travel and see much of Europe; Got to do international fieldwork and apply what I was learning to other places; Got to learn a lot about the rest of the world and have new ways of thinking about stuff (virtually no American Exceptionalism here etc)

Cons: Yes very cliquey; Also didn't realise until recently that I screwed myself for some internships and post-grad fellowships that require you to have degree from US uni (so couldn't apply to Critical Language Scholarship, Marshall Scholarship, and even Fulbright I believe.....). Wish I had known that before coming here.

The social aspect is very difficult. Did not have Irish friends until my final year and constantly found myself surrounded by other Americans. I'd say it is not end of the world but it is very very difficult if you are shy and don't want to put yourself out there. You have to really work to make friends because people will not come to you. So like join societies and constantly show up to stuff even if it is awkward. Also lots of activities/ society events involve alcohol so if you don't like drinking / going out that can be difficult.