I haven't read a ton, but I started with Civilwarland in Bad Decline, though I think "Pastoralia" is the best thing from him I've read so far.
Boom! Finally started Tenth of December
and thus far the stories have been quite good. Looking over the Saunders I have read before this one (really only three or four stories it looks like), he's been mostly hit for me. I don't remember much of "Sea Oak" but it stands at the weak link in my faded memory.
This collection is being called his "most accessible" from what reviews and stuff seem to say. I don't think he's super difficult to penetrate (though certainly "CivilWarLand" and "Pastoralia" do not exist as the most conventional of narratives), and thus far these stories seem more in line with his other stuff. Look forward to reading more.
EDIT: Apparently this guy is also compared to Vonnegut a good deal. I haven't read Kurt's stuff, but I'll take others's word.