1) The EU now officially recognizes the Pound as a currency of the EU. This is little more than slight of hand, and has been unofficially recognized by the EU for quite some time.
2) UK industry cannot be 'discriminated against,' particularly the financial sector. For example, financial firms in London will be able to trade in Euros. Actually, it was already this way, so this is just another item that went from de facto to de jure.
3) Fewer benefits for EU 'citizens' who move to Britain. Those who move to Britain from other countries in the EU will now have to wait four years to get any benefits. This should put an end to those who came to Britain to take advantage of the National Healthcare Services for just a few months. Cameron also secured a deal where child benefits will be reduced for those who are sending their money to children in other EU countries.
This is a some what substantive change, although I believe the biggest foreign welfare abusers in the UK come from outside of the EU.
4) No more "ever closer union." This is also somewhat substantial. The goal of an 'ever-closer union' is written into the EU Constitution. Ever-closer union is understood to mean that the goal of the EU is to merge the states politically, to make some kind of 'EU superstate.'
Britain has already had a somewhat special role in the EU, and it was already somewhat understood that Britain was not part of an 'ever closer union.' (This is why British MEP's are often shut out of decision making in the EU Parliament.)
Still, an official declaration that the UK is not to be a part of 'ever closer union' could be reassuring to many.
What's missing from this bill? First and foremost, border control and free movement of people. Anyone with an EU passport still has the right to come to Britain freely, work in Britain freely, and live in Britain freely. That's going to be a big problem in the coming years, because all these 'migrants' coming from middle eastern countries can (and will) come straight to Britain as soon as they get EU passports. The biggest gripe of Britons has been migration, and I don't see this deal doing terribly much about it.