Like littlesilver ours wouldn't feed us as it claims, though we eat a lot of veg. But i do like that we end up eating veg we wouldn't have other wise, it's spanking fresh (and there's quite a lot, that having been brought up on home grown veg, i just won't buy in the shops) and supports a local organic farm. It's family run and planning a new straw bale building so they can get school groups in etc.
We collect, they don't deliver, but like to wonder round the farm, especially as stuff that there is plenty of you can often have as much ah you can be bothered to pick. I think ours works out really good value. It's about a quid a day. Back in april may, when we started, it could be a bit sparse, but now we get tons for our £7! Also meeting the other people when we collect is nice (they have bbq's too but we haven't made it to one yet). Also you can pick unlimited herbs, and, in season, flowers.
Re menu planning i just wait till we get it and then plan. Books like tender by nigel slater, or jane grigsons fruit and veg books will give you endless ways to use the veg in ways that really let them shine. I guess in winter it might be endless turnips or whatever, but i love cooking and grew up with food being very seasonal like that so actually quite like the challenge.
I think you have to decide why you want a veg box, and then find one that does that. For example, although your local farm shop delivers them, is the produce local? Does that matter to you? I certainly wouldn't subscribe to some of the other schemes but love ours.