XV and XII seem almost diametrically opposed with certain people, as I really like XV and consider XII completely unplayable. XIII also, but to a lesser extent.
Eh, I think I'd put both in the same ball-park. They're both relatively flawed, particularly in the story department, but their gameplay and worlds - as well as a few memorable characters - make it worth the journey. Yet that gameplay also doesn't seem to sit well with people for various reasons...that I personally don't really get. FFXII I better understood the complaints, but I always felt it was reasonably enjoyable, and a nice twist on the MMO-esque gameplay that usually bores me to tears. If anything, it gave me an idea as to why MMO players put up with the classic psuedo-turn-based combat, since it seems to be more interesting when coordinating with a group rather than fighting solo. FFXV, though, seems pretty fine to me. Reminds me a lot of Kingdom Hearts in the best of ways. Reasonably fast-paced without becoming unwieldy or repetitive; more than a few interesting monsters to fight, especially during hunts; and allies that you don't have to rely on, yet are still useful enough that I don't feel like I'm better off just playing without a party like I do in most other Action-RPGs. And I just loved exploring the fantasy world they set up. It's close enough to the real world that the fantasy twists added a sense of surrealism, and made it a lot easier for me to understand what it must be like to live in their world, often without forcing me to sift through long-winded explanations and dialogue trees (a frequent point of contention I have with Western RPGs, especially considering how many do very little to make their medieval fantasy worlds stand out).