I've been over for two short trips over the summer. I really like Bern and Zurich, and would definitely suggest visiting Thun/Interlaken as the scenery is stunning! Was less fussed about Basel but then again I didn't have much time to explore and I have friends who rave about it.
Can echo the sentiments about how expensive it is to eat out - I largely lived off homemade sandwiches and the occasional takeaway schnitzel.
Having fallen foul of it before, ensure you book all trains (tickets/rail passes) in advance before you travel as it is very very expensive to buy on the day. However, second time of asking I was able to buy much cheaper, print at home, tickets between the major cities before I left the UK.
Probably won't suit the time you're travelling, but would recommend taking in a football game while you're there. Considering how expensive Switzerland is in general, the football is surprisingly cheap. Once more, you can drink (and smoke if you're that way inclined) on standing terraces and most teams have a vibrant ultra following which is good entertainment value in itself. I've had good days out watching BSC YB at Wankdorf and FC Thun at the Stockhorn Arena which I would both throughly recommend.