I've read them, they're actually pretty good! They do lean into the Christianity at some points but they aren't as egregious as most Christian lit. The author balances it well with Celtic druid beliefs and I don't remember them being too over the top religious (I haven't read the whole series in a long time but I did reread Taliesin last year).

Taliesin was probably my fave of the series, it has a lot of interesting detail on Celtic life, druidism and also has an interesting beginning storyline set in Atlantis. I enjoyed it, and the Christian stuff only comes up towards the end and is fairly easy to skip if you want.