The town itself is well preserved, and retains an atmosphere of being awake/interesting, even in Winter when its neighbours resort to sleepiness.
Dartmouth Castle is in good condition and gives great views back on the town and out to sea. There is a museum, and river cruises in summer.
It is really nice to wander the streets and soak up all the history. They are narrow, and many are pedestrianised, so the town retains that old world charm.
For us it had a sort of buzz of activity about it, which the other coastal resorts just lacked a bit.
When the yacht races occur in summer, it gets quite crowded.
Quick Tips:
There is a lot of fascinating maritime history here. The pilgrims set out from here via Plymouth, to colonise the New World, as did many other voyages of discovery.
The Normandy invasion force (or part there of), also left from here in WWII.
And, of course, the seafood is fresh and excellent.
Best Way To Get Around:
A return ticket from Paddington is GBP 67 to Totness. From here you take a bus. The journey takes about 3-4 hours.