I stayed at Sokos hotel Vaakuna for one night during a business meeting in early August.
The hotel is centrally located, with an apparently fresh facelift, very attentive and pleasant staff, and also easy access through an underground parking facility (great during winter as well). I stayed in room 507 with a scenery overlooking the central market square.
Extra points for the surprisingly decent gym with basic exercise machines.
Otherwise, like most S-hotels, the rooms are very standard and somewhat boring. An issue that is difficult to avoid in normal business hotels. Extra points for easy access and free wifi.
The main question: Would I stay here the next time I come to Vaasa? Absolutely.