He's a super mainstream director with huge budgets. It's superhero fans who made him famous, movie nerds like him up to Memento (his first movie with a real budget) - Insomnia is not bad but a real movie nerd watched the original and knows Nolan butchered it by inserting American moralism (making main character tragic and sympathetic because American audiences are driven by emotion and must empathize with the main character).
His big movies are only "brainy" if you compare them to Marvel and Fast and Furious movies.