I've written a total of five novels and have queried agents on most of them. But the weird part is, writing a query letter to a literary agent is harder than writing the novel in the first place.
Why is that?
First, I think when one spends months and months (or even years) writing your book, to summarize it into a handful of sentences is a challenge equal to that of hand-to-hand combat with a gladiator. There's so much to put in, even though you can't. Second, there's a lot of importance to the query letter. It's a lot like dating.
Very, very few agents will take a look at your manuscript unsolicited. And with the cost of postage nowadays, I wouldn't want to shell out that kind of dough, because not only are you paying for the novel to ship sent to the agent, you'll have to pay to send it back in a self-addressed stamped envelope (or box in this case of your manuscript). Of course, you could e-mail it, but no agent will open an e-mail with thirty to fifty attachments. The agent will probably hit the DELETE key.
So, my fellow writer, you'll need to write a query letter.