It's actually not very sour at all, and each batch I make gets less sour (I re-use the same culture from the bottom of one of the bottles from the previous batch each time). The lacto bugs are probably slowly dying off.
Anyway, as best I can describe it, it's a sort of a musty, leathery, catty, cardboardy flavor? Bizzarely enough, they don't taste like off flavors. Also, I'm sure it's not oxidation because I've made other beers in the same equipment the same way and they came out fine. I like the way it tastes, it just needs something to balance it out.