This list is restricted to "epicish" fantasy, which by my off the cuff definition generally involves a secondary world and warfare based on sword and spear.
The reason for such restriction is simple - it's my favourite kind of fantasy, and were I to include YA fantasy, urban fantasy, paranormal fantasy, romance fantasy etc the great majority of the the books below would be swept off the table because the truth is that "epicish" fantasy is a niche genre and sells far fewer books than the kinds of fiction I just listed.
I crowd sourced this list over at r/fantasy and if you have a debut book you think fits, please mention it in the comments.
The numbers in brackets are the number of Goodreads ratings the book has. Since this is directly related to sales it is a clear indication of the "size" of that debut.
I have included three titles that aren't really "epicish" but don't seem to fall into the other categories I mentioned either. They are probably close to magical realism, which crosses over well into the general readership and gets big sales. I've left them (shaded red) as reminders that the kind of fantasy shown here constitute small fish in a big pond!
Where I had more than three I have stuck to the top three except in cases of ties.
2007 - The Name of the Wind (449K)
2008 - The Way of Shadows (114k), The Warded Man (77k)
2009 - The Dwarves (7k), Lamentation (3K), The Adamantine Palace (2K)
2010 - The Hundred Thousand Kingdoms (32K)
2011 - The Night Circus (474K), Prince of Thorns (63K), Blood Song (52K), Theft of Swords (37K)
2012 - Malice (8K), Throne of the Crescent Moon (8K)
2013 - The Golem and the Jinni (71K), Promise of Blood (25K), The Thousand Names (12K), A Crucible of Souls (5K), The Grim Company (5K)
2014 - The Emperor's Blades (23K), The Goblin Emperor (14K), Traitor's Blade (9K)
2015 - The Library at Mount Char (16K), Dawn of Wonder (12K), The Grace of Kings (7K)
2016 - Hope and Red (1K), The Summer Dragon (1K), The Crimson Queen (1K), Benjamin Ashwood (1K)
2017 - candidates include, The Bear and the Nightingale (14K wow!), Kings of the Wyld, Blackwing, Godblind, The Court of Broken Knives...