Riga
dodgy as fuck, was afraid of my own shadow
My girlfriend is Latvian so I've been to Riga twice in the last few years for a few days at a time. It's an extremely unfriendly city. The customer service is non existant as people shrug their lives away.
Fortunately, as I said, she's from the country and speaks Russian so it's easier to get by but I'm not sure how I'd get on with a group of English only speakers.
The old town is fine, not much bother there but around the main bus stop area is horrible, full of drunks and homeless.
However, there is a Japanese restaurant chain called Gan Bei which I must always compliment, great food and incredibly friendly staff. There's one in the central station and a couple of more around the city.
Did you venture outside the city centre at all? I had to meet relatives in the suburbs of Riga. Just rows and rows of apartment blocks, it's strange not to see houses and estates at all in the suburbs.
The zoo is very much like the city, messy. There's not real route in the zoo, you can miss so much by not going down a path that looks like it's going nowhere.