Unlike most long-running urban fantasy/paranormal romance series -- which I find myself tiring of 4-5 books in (*cough*The Hollows*cough*) or where the heroine makes really dumb decisions and winds up with a love interest I don't like (*cough*Southern Vampire*cough*) -- this series has stayed consistently fun to read, though not outstanding. It's not full of badly-written fanfic-style smut. There's real romance, suspense, and occasionally scary bits. The characterization is consistent, the love interest is actually likable, the side characters are a blast, and the author doesn't shy away from the consequences of her characters' actions.
I found River Marked to be one of the better entries in the series so far, even though it mostly takes place away from the normal center of the action. The big bad was scary, truly scary. I really enjoyed the Native American lore, and finding out a bit more about Mercy's parentage.