There is *no* reason why, if you want to buy Locke and Key, you shouldn't buy the hardback edition.
The binding cover is beautiful - the picture on here does not do it justice. There are nice sketches of the layout of the Keyhouse on the inside covers to front and back, as well as some great cover / concept images at the back.
The introduction by Warren Ellis is sharp and witty. Joe Hill's storytelling is, as ever, flawless, and the edgy graphics complement the dark and complex story fantastically well. His characters are believable, the dark fantasy is plausibly explained, and Rodriguez' artwork helps bring it all to life - it's the minor details, such as the sound "effects" when characters are opening doors, the non-verbal actions - that help to make the depth of Locke and Key come to life.
I must point out that, at this time, the paperback edition is also slightly more expensive than the hardback - so why not treat yourself to a beautiful edition that will stand the test of time - as you will want to read this again and again.