Getting a UK passport and getting UK citizenship are different things as far as I am aware. You can have a UK passport but not be a citizen. So you don't have to give up your original citizenship (not that I think you would have had to anyway).

Having the passport basically means you can live and work in the EU indefinitely. Certainly a good thing and there aren't any bad "side-effects". Just make sure you enter and leave countries on the same passport. A friend of mine entered the UK on a Swiss passport and tried to leave on an Australian passport. Their response was something like "How did you get in to the UK? You're not supposed to be here"