Lively, fun and energizing. Guu is all about the atmosphere. Go there to have a good time and feel at home.
The food is also really good but a little pricey for tapas. For a group of 6 you have to order 2 or more of everything if everyone wants a good size portion. I also recommend getting a few drinks, they're all really nice and have some interesting flavors and what's tapas without a little alcohol.
Servers there are always in a good mode and are excited to serve you. The only problem is there might be a language barrier if you don't speak Japanese or Korean in some cases.
I definitely recommend trying guu at least once. But make sure you go there before the rush cause you'll end up waiting 20+ minutes.