It depends really on what interests you with Geology. Each year is split into large sections (for my exam board atleast) with the first year being tectonics and rocks (e.g. types of rocks and environments of deposition) then in the second year is sort of like applied geology (e.g. mining, water resources and engineering geology) and fossils/past environments. If one of those you don't like it can be a bit hard, I don't like the fossils part much which I am currently doing since there are so many types and there are so many key terms you need to learn for each.
As said above it depends on what you are going to do later on as well. I was interested in a geology degree at the start of the year but now applying for civil engineering which geology helps a lot with in the applied geology section.
I was interested in the A level because in geography I loved the physical side of it which geology puts more detail into and then more.
It does open a lot of routes for later careers which it can relate to. People in my class are going on into a range of things at uni including other types of engineering and some in english or humanities, about three in my class are going to do geology at degree. One about it is that not many do it (there's only one class in my current year and then 2 in the year below in my 6th form) so you will get better teaching since there's more attention to you and also less in workshops etc.