Just finished the game (including the DLC which is expansion-size). I would not call it an RPG (you eventually unlock every skill), but it plays similarly to Witcher 3 with better combat, story and loot system. However, W3 definitely wins on sheer amount of quality content (side quests), overall size and C&C (which is marginal at best in Horizon).
Also, for better or worse, this game is the embodiment of PG-13 content. Everything is mild and inoffensive, violence is tempered, there is no swearing, etc. I found this a breath of fresh air after overdosing on edginess is some other titles, but your mileage may vary.