The series does meander around the middle. Misunderstanding based conflict is Riordan's middle name. But I think the finale was great, it was suitably epic and became more mature in a sensible way. Not sure if I would recommend you finish them though, its been a long time since I've read them.I read the first three Percy Jackson books around the time the first movie came out (never watched it). I remember enjoying the first two but getting kind of tired of the series by the third for reasons I don't really remember anymore. It might have been that the plot started to revolve around annoying misunderstanding based conflict between characters, but I can't say for sure anymore.
I never did enjoy the steampunk aesthetic. I don't think Sanderson's style really suits having two middle-aged men as the main characters.The Mistborn books are definitely not as good as the original trilogy.