Starting out with Graphic Novels

It's an unfamiliar area for me - graphic novels. I know very little about Marvel or DC or the tangled continuities of the superheroes, and it's difficult to know where to start, with such a wide variety of graphic novels out there.
When I was an archaeologist, though, one of the diggers used to buy a 2000AD comic for everyone in the site hut to pass around (yes, we were that poor!), so I've known about Judge Dredd and Strontium Dog and Nemesis the Warlock and so on for a long time. My favourite, though, was Slaine, and as archaeologists with an interest in the Celtic Iron Age we were all impressed with the amount of research that had gone on to write that one.
So when I was in Manchester over the weekend, we stumbled across a Forbidden Planet - and kind of couldn't pass the door until we'd explored the SF and Fantasy goodness within. Down in the comic section, we came across Slaine, the Books of Invasions - wonderful artwork by Clint Langley, with the story by Pat Mills.
And then I went a little mad.
Another comic I had come across in my youth was Green Arrow - I used to get that from a little comic shop near Scotland Yard when I worked in London, and I'm aware of the new US TV series, though I haven't seen any episodes of it yet. There was The Longbow Hunters, with Oliver Queen looking just as I remember him, with the yellow beard and the Robin Hood hat. And the longbow, obviously.
Neil Gaiman is one of my favourite authors, and I knew he'd started off in comics. In fact, back when I was reading Green Arrow, I also picked up Black Orchid - I had no idea of who the writer was at the time, because I'd never heard the name before, and it didn't stick in my memory. Then I started reading books like Neverwhere and American Gods, and did some reading about Neil Gaiman's career - and remembered how much I'd enjoyed Black Orchid. I didn't find that this weekend, but I did find Marvel 1602 - in the hands of such a master, how can I go wrong?
And finally, I'm dabbling at the edges of Steampunk. I love the costumes, and the alternative realities, and I had heard of a character called Inspector LeBrock of Scotland Yard. Who is a badger. In an alternative 'Victorian' London. They had Grandville, the first in the series, in which the Inspector goes to Paris.

I have the feeling there is a whole new world opening up before me....