I just started reading the series. Started just with the first one. Really enjoyed it, it reads like an action movie. Reading the second one. Starts a bit slow, but it's starting to suck me in as well. (don't remember the names, the books have such weird names :))
If I end up enjoying it as well, I'll just keep going probably. This post makes me want to read them all :)
The culture series? It's not outright said they're human, but they're clearly human. And they outscale basically every single thing in the universe. Or at least in the first few books. Might change later.