Have only just seen this. I lived in Hitchin, Stotfold (village near Letchworth) and now Royston, though not Letchworth itself.
However, I end up going to Letchworth quite a bit one way and another.
The shops there are quite an eclectic mix - your usual high street stuff, but also quite a few independent ones (can recommend Tom's Deli - good range, "old fashioned" service, and the traditional sweet shop in The Arcade - think it's called Annies). These days there are a few more pubs and bars in the town centre itself, though I've never been in them .... but can recommend an Italian restaurant called L'Artista, very reasonable, very family friendly, large and generous menu.
Just oustide the centre you have Sainsburys which is being refurbed and extended, plus the North Herts Leisure Centre, half way between Letchworth & Baldock. It has a swimming pool, courts, gym etc. In fact there's quite a few gyms in and around Letchworth. There's also an open air pool in the summer (ditto in Hitchin).
Letchworth is equadistant between Hitchin & Baldock which both also have a lot going for them. Hitchin in particular has a huge range of amenities, and a really good selection of restaurants.
I'm afraid I can't speak for Letchworth schools but the town itself I really like. Both Letchworth & Hitchin have always felt very "safe" to me (though like anywhere they have their less attractive areas) with a good vibe. As I'm sure you know, you'd be on a reasonably quick train route into London or Cambridge (great shopping .... yes, I'm obsessed with shops), and on the A1, so communications are very good. Similarly, you only have to drive 5-10 mins and there are plenty of villages with nice pubs, attractive countryside and so on ..... so you have the best of both worlds.
If there's anything more specific you'd like to know, ask.