It can be both fun and a pain, sometimes at the same time. You just have to make the most of it at the right time.
All of my classes were fun to be in, and while I was the quiet guy that no one really knew the name of in Year 12, that changed in Year 13 and that's when it got really fun. Jokes at the right time are great (though not when everyone's seriously stuck into classwork), playing hangman during breaks, debating about stuff, there are a lot of interesting things to do. And if there's someone you're interested in, get together to study and get to know them and something might happen.
It is also a step up, but a lot of the step up is adjusting from how you were learning before to how you'll be learning at A-levels. It requires a lot more independence, time management, etc. I'm not one for timetables but a general timetable of what I should know by when, what I should start by when was helpful. Just put the work in, do past papers and develop your understanding of the topic.
And revision guides, where applicable, are amazing, they're definitely worth investing in.