It's reflective of everything he's done before and everything he did after. Once you read the series in the entirety you don't really need to read anything else by him. Though it's best read as the Part 1 to The Filth's Part 2 and Flex Mentallo's Part 3 Climax.
I've read the first 6 or so issues and found it quite boring (issue 2 was fantastic but the rest were meh). Does it improve over time or am I just not gonna get into this series?
It changes gears a lot, over the course of the comic. It'll be glam action for awhile, it'll be gothic horror, it'll be comedy party or weird everything's-a-metaphor time.
Some folks find Volume 2, the America section, to be easier to get into, because it's more actiony and glib, at least on its surface.
It already changes gears a lot in those first 6 issues.
I do wonder what about it was boring.
'The marquis. Well, you know, to be honest, he seems a little bit dodgy to me.'
'Mm,' she agreed. 'He's a little bit dodgy in the same way that rats are a little bit covered in fur."
One of the scariest realizations, looking back on the series, is how close to my age/generation Dane is in the series. I had such a much younger brother read on him when the series was coming out. He's The Kid. Another realization, then immediately followed: How much I undoubtedly sounded like (and postured like, and finally chilled out like) Jack.
Yeah I don't think The Invisibles has to be" worked up to" really - just dive in! It was the first thing of Grant's that I read (well apart from some stuff in 2000AD but that's not really the same) and I was blown away.
Though I did begin smack-bang in the middle with Counting To None so I would advise if your a little unsure you could start with Volume 2 as it is more "actiony" but has plenty more going on too. If you were a little underwhelmed by the first volume try Bloody Hell In America which is the small 4-issue beginning arc to Volume 2.