Though I have been living in Riga for many years now, I haven't been going to restaurants much (if at all recently), so not sure what the best places are these days.
We have some work colleagues coming in, and are looking for a place for dinner for about 20 people.
Something more on the casual side, rather than fancy dining. Medium expensive. A place you could feel free to get up and move around and go to the bar, rather than sit in one place. Preferably Old Riga or not too far away. Preferably a place with some set menus, and we could order a bunch of different things in advance. A private room might be good, but not essential, so long as the place isn't too noisy.
Something like Folkklubs Ala, maybe (but I'd rather not go there, last I remember the service there wavered between extremely slow and non-existent). Stargorod was a wall of noise the last time I went. Maybe Portofino, or Rozengrals, or Naples on Andrejsala (though 20 there might be a tight fit).