Physics is a bit different to the other sciences at A level in that, rather than introducing lots of new topics, it covers a lot of the same stuff that's in GCSE but in more detail. For this reason, I have found it easier and more enjoyable than GCSE. Concepts that baffled me at GCSE (such as electric circuits) have become very clear due to gaining an actual understanding of what's going on (whereas I found at GCSE you skim the surface and have to try and remember and understand things without the foundation knowledge of what's really going on).
Physics was my worst science at GCSE (I got an A* but that's the equivalent of an 8 and I've no idea if I would have got a 9 if it had been possible when I'd done it) but now I love it and get the best A level scores my teacher has ever seen.
In summary, if you're interested in it and it's what you want to do, do it.