I don't want to be unnecessarily discouraging so I'll just say middle school curriculum is definitely information-light. The teacher makes a big difference, especially if they're capable of adding extras info or a answering questions, or if they make the lessons themselves.
However, based on my limited experience it seems like HS is at least a refreshing break in the monotony,if not challenging. Common core is less prevalent, there's a faster pace in the honors courses (of at least faster-feeling, no promises), and there's less handholding - assignments are due when they're due,no question, and your goodness sake's you can't retake a math test six times even if - gasp! - you might get a B or feel bad about yourself. Biggest pet peeve, BTW.
Honestly, I find myself asking these same questions with HS coming up. When do I settle for challenging enough? When is it just too late, wait for college? Does our school even have anything challenging to offer? Is it alright if the only challenging class is an elective and maybe a class with a good teacher? I can't say. But I can hope for the best.
Middle school might not be challenging, but it's fun. Especially those electives, at least if they're taught well. (I guess I can't assume that, can I? Nothing ever is...)
Good luck!