The main benefit from the backmatter is understanding the context of the other families and their political relations with the Carlyles. It's definitely possible to read Lazarus in trades and still get all of the fundamental plot points but the backmatter in the single issues definitely enriches your understanding of the world Rucka & co have created. If you also read the HC vol. 1 supplements you get even more info which gives you hints at possible conflicts down the road.
I don't agree with whomever called the art or world of Lazarus "dull." The artwork is deliberately gritty, grimy and appropriate for a dystopian setting such as this. I'd be interested to hear how the critics reacted to Lark's DD run or his collaboration with Rucka on Gotham Central. The art is definitely in line with those books and works well for Lazarus. If you prefer bright, cheery retro super-hero art and stories , this book is definitely not for you.