I did Berlin-Szczecin and back in a day a couple of years ago. The journey takes about 2.5 hours. It's an irregular service though with up to 3 hours between trains. Szczecin is pleasant enough, and the town centre is about a 15-20 minute walk from the main station (Szczecin Glowny). As I was travelling with a friend, we did the entire journey using the Brandenburg-Berlin ticket (starting at €29 for two people). North of Angermünde, the line is obviously a shadow of what it was. The stations are basic, but many have the old, very grand, station buildings in situ, now sadly shuttered and abandoned. The ride across the German/Polish border was very lively, with the DMU bouncing around on delapidated track. You should be aware that owing to engineering works, direct trains depart from Berlin Lichtenburg (3 per day with an extra on Fridays). There are connections available at Angermünde from Berlin Hbf/Gesundbrunnen for the remaining services. The current timetable is valid to 11 October only, so I would reiterate NicholasNCE's advice to check journey details before you make any plans.
