I'm from Galway and live here, so I might be able to give you some more tips.
The food here is very good, with a wide variety on offer.
If you're into seafood, we've some of the best in the world. Hooked (
http://www.hookedonhenryst.com/) is superb. It started out as a fish and chip shop but has grown in to a proper seafood restaurant. It's very casual and doesn't take reservations for parties less than 6 so try to get there before the evening rush.
In that neck of the woods, you'll find The Universal (
https://www.tripadvisor.ie/Restauran...n_Ireland.html), it's an excellent wine bar that also does food. It has a small kitchen and a small menu, but in my opinion it's doing some of the best food in Galway, and hasn't yet been overrun by tourists.
A few doors up from that is Kai (
http://kaicaferestaurant.com/). It does excellent brunch and lunch, the a la carte menu is good but I think the Universal is better.
Ard Bia is also very good for brunch/lunch (
http://www.ardbia.com).
Cava was mentioned above, it's nice but there's a smaller tapas bar which opened recently called Sangria (
https://www.tripadvisor.ie/Restauran...n_Ireland.html) which is much better.
Rouge was also mentioned, I would avoid it. The quality has really slipped, it's not worth a visit.
If you're in Galway on Saturday morning, pay a visit to the weekly market outside St Nicolas' Cathedral.
In terms of activities, there's plenty listed in website you linked. I would recommend going to Salthill, it's about 2km from the city centre and on the seaside. It has a 4km promenade which is nice and scenic to walk. There's a great swimming spot and diving tower at Blackrock, the water is lovely at the minute and it would make a nice break from the city.
Here it is:
If you have a car, head west to Connemara. It is really beautiful. Drive through the Inagh Valley, it's jaw dropping and you can pay a visit to Kylemore Abbey at the other side of it, or you could climb Diamond Hill in Connemara National Park which gives you spectacular views of the surrounding Twelve Bens (it's not really a climb, more of a walk).
Inagh Valley:
Top of Diamond Hill:
The Aran Islands are definitely worth a visit, however under no circumstances should you go there if the weather's bad. It's not worth it. It's a full day out, so might be a bit much with only a 3 night stay.
If you're heading back from Connemara, take the southern route and visit Dog's Bay. It's a spectacular beach with white sand and turquoise water. It's close to the village of Roundstone which is nice if you want to stop for lunch, or you could travel a few more miles down the road to Ballynahinch Castle which is has some lovely walks on it grounds and does a great lunch.
Dogs Bay:
Ballynahinch Castle:
Finally, people do not visit the west of Ireland for the weather:) We get copious amounts of rain here, so bring appropriate clothing. That being said, the forecast is looking settled for the weekend so hopefully you'll get some decent weather.
I've only scratched the surface, but if you've any specific queries, please let me know and I'll do my best to answer them.