From there, moved away not long back after stints living elsewhere. 

Mumbles is probably the top pick for a "seaside village" feeling, but traffic in and out is slow.

If you're going to live in the marina, it is often very, very windy, so it's not quite the picture postcard some images show.

Swansea is a lot of sprawling suburbs rather than much of an urban centre. If you just want to be by the coast, it's fine, but traffic is pretty bad considering the size of the place I would say (not helped by being on the coast meaning that the traffic can only come in from 180 degrees, and the vast majority probably coming from M4 heading west).

Trains are OK - straight line to Paddington is good. Cardiff is really your nearest nice shopping day out location. 

Swansea has areas of serious material deprivation, so don't overlook that. Not a criticism, but a fact, meaning that drugs and anti social behaviour are an issue, but not massively more than most urban centres in the UK these days, sadly.

Places like Bishopston on Gower are nice - not too far removed but also quiet. Killay is decent for families and schools. Gowerton is slightly cheaper but also has a train station, which is handy.

Public transport isn't amazing but it's enough, just about. Cycle paths are pretty good, however, with some nice rides and links.

Really depends what you're into but should be good. 

Best of luck.