Long posting alert .....
As it happens the first time we went Menorca 10 years or so ago we stayed in this hotel, but I'm afraid I can't really give you any useful info on the hotel as looking at the website it has been completely refurbished, and to quite a high standard! Previously it was pretty old fashioned and a bit worn around the edges but it seems a lot of money has been spent on it to bring it bang up to date. One thing I do remember enjoying though is sitting on the outside terrace with a drink watching the shipping and sail boats going in and out of Mahon harbour ... very relaxing!
Regarding Es Castell itself I seem to remember it had a few bars and restaurants (but not lots) around an attractive small harbour which is a few minutes walk away from the hotel. Think there was even an English pub style bar ('The Teapot') if that's your kind of thing. It was a pretty quiet place which only really came alive in the evenings when it was quite popular with tourists and locals alike. Don't seem to remember there being any nightclubs/disco's (showing my age now) so you didn't have hoards of hormonal stag and hen do's stalking up and down looking for the next drinking hole! Also there weren't really any beaches, just a couple of small sandy inlets which again were quite popular with the locals, which was quite nice actually. Also I believe Es Castell was a garrison town when the English were controlling Menorca so if you walk around the town centre you can see examples of Georgian architecture which felt a bit weird.
One of the advantages of Es Castell is that it is fairly close to the old Menorcan capital of Mahon and is walkable in 45 minutes to 1 hour or so (depending on the route and how many bars you stop at). Of course there are always the buses and taxi's if you don't feel like walking! Mahon is quite an interesting place to spend a day or so, a visit to the Xoriguer gin factory is highly recommended
You can also do all the usual holiday stuff from there, boat tours, shopping, etc
When we went we were half board but I seem to remember we did struggle a bit to find places open for food at lunchtime, if we went again would probably do full board/full inclusive. Also wouldn't want spend 2 weeks there, I think 1 week would be enough.
We've been back to Menorca (but not Es Castell) quite a few times now as we like the quiet, laid back nature of the place. If you want a quiet holiday in a bit of 'backwater' location then I think Es Castell would be OK, especially seeing how the hotel has been updated, it looks far nicer than when we were there. If you're hiring a car even better as you can get out and about much easier.
Bear in mind that we went there quite a few years ago so things may have changed a lot, but overall I seem to remember having a very pleasant holiday there, in actual fact seeing how well the hotel has been refurbished may even consider going back there next year, we were just wondering where to go!