It's still hard for me to believe Funeral is The Arcade Fire's first album. There are great debuts like Guns N Roses, Hendrix, etc., but I don't know if I've ever heard anything so sophisitcated and majestic from a band on its first outing. The Velvet Underground had a landmark debut but I can't say that it's as moving as Funeral.
Funeral is probably not my favorite debut album (that might go to Liz Phair's Exile in Guyville), but at this moment I'd have to say it's the best/most accomplished, or in a really close tie with Patti Smith's Horses, which is also pretty damned phenomenal.