I've finished it numerous times.
I have the original and Binding of Isaac: Wrath of the Lamb.
They were fun for a couple of playthroughs, then I got bored.
200+ hours here and still counting, can't get bored of it. Rebirth is coming out and it's gonna be so fun man. It's BoI + WotL x2 size. 400+ items and more endings. Looking forward to it. Bindingofisaac.com