What are some murder mysteries along the lines of Agatha Christie?

I've recently read a few Agatha Christie novels and while I enjoyed them, they felt a bit light (as in, lacking a lot of real substance and feeling like a fairly casual read). Does anyone have any recommendations for murder mystery novels with a similar vibe and setup to an Agatha Christie novel, but with a little more depth (more realistic characters, more emotionally investing, a more complicated crime, maybe just longer, etc)? Or, a murder mystery that you really enjoy and feel stands apart from the genre.