Karen's is the best deal in Galway, bar none. The guest house is separate from the host's apartment, affording excellent privacy, and there is parking right by the back gate. The kitchen, bathroom, and bedroom are clean and well-outfitted, and the bed's a perfect fit for two.
Karen and Sean are very friendly, and provide all kinds of useful tips for the traveler new to Galway. May we recommend The Quay Kitchen and Kai as the best lunch/dinner food in town, with wonderful traditional music at the Crane Pub.
Make sure your satnav/Google Maps/GPS has good connectivity, though, because Irish lanes are narrow and not always well marked. Karen's extremely quick to respond, though, in case you get confused or lost.