Zagreb offers both beautiful nature, good dining, and excellent clubbing.
Zagreb can be visited all year round. Every season has different sights and I haven't yet decided which I prefer . . . but if you're single, you'll enjoy the girls on the streets of Zagreb during the summer for sure.
Exchange currency to euros and, if at all possible, pay with that through your stay -- you'll get a MUCH better rate than at the official exchanges.
Best Way To Get Around:
Streetcars run often and cover most areas of the city that tourists could possibly visit. I'm sure they supposedly cost money, but I have yet to find out how and where to pay, so I ride for free!