I spent three days there, not on a stag, just a quiet city break.
The city is pretty and historic but can be walked in a day. The museums aren't up to much.
Drink is cheap enough as previously alluded to. I wasn't too impressed by the restaurants I was in. The service was still quite eastern-bloc and still reminded me of a tour of Czechoslovakia and Hungary.
I found the place a bit sleazy ... there were a lot of thuggish looking young guys driving around in big cars with tinted windows. Apparently the Russian mafia takes 10% off the top of most shops in Riga, and that's where the money from all the night-clubs and red-light is likely going as well. The first ad you see at the airport is for a strip-club.
I stayed in the Karavella hotel in the suburbs. A grim old intourist joint, not recommended.
So general view it's good for stags but for a city break I'd chose another location.
Gearoid