I think I’ve mentioned the books here before (and if not, shame on me). Regardless, the Shadowmagic series is a worthwhile read. Fun and action-packed, it takes the “fish out of water” fantasy trope and turns it on its ear, giving us a protagonist that isn’t an idiot and knows full well he’s out of his depth.
Plus, it goes into Gaelic mythology which never seems to get enough attention, in my opinion.
Check out the books by John Lenahan if you have not already. Available in paperback and Kindle.