Man, I'm glad I went in blind with 'Odd Thomas' before checking out any of the adaptations. That first book, especially, hits different when you haven't seen a face for the characters yet. Koontz builds this whole quiet, dusty town vibe around Odd and Stormy that just gets under your skin. You really feel the weight of his 'gift'—or curse, really—because the writing is so grounded in his everyday struggle. The later books wander into bigger, weirder mythologies, which is cool, but nothing beats the raw, intimate feel of that initial mystery.
I tried watching the movie after, and while it's fine, it just cemented how much of the series' heart is in the prose. The deadpan humor, the little philosophical asides Odd has... a lot of that texture got smoothed over. If you're the type who likes to form your own mental pictures before seeing someone else's interpretation, starting with the books is absolutely the move. Plus, you get to experience that infamous ending totally unspoiled, which is... yeah. Brutal, but in a way that sticks with you.