I will be going there for a couple of days in a few weeks.
1.I would take a walk from Waly Chrobrego all the way to Old Town (quite small) with the Castle on the way. This path is along the Odra river, so it should be nice and it will take you a couple of hours with stopping for beer and pics. There are some spectacular building: starting with the Provincial Government building, Contemporay Theatre building, maritime Museum and finally Maritime University.
2. Grunwaldzki Plaza is a must see IMO
3. Boguslawa Passage with small galleries and pubs. Fanaberia tea house is worth a visit.
4.if you really interested in war times there is a bunker tour which starts at the train station (2 hours)I haven't seen it but Szczecin has apparently a lot of bunkers and underground tunnels dating back to German times
there is more......it depends what your interests are.