I don't know how big Dungeons & Dragons got in Japan back in the 80's—hell, I can barely tell how big it was in my high school less than 10 years ago—but there was clearly some market. Ys, which is incredibly hard to search for on google if you only use that name, is where the line of D&D-style high fantasy anime begins, followed up shortly with the even more Western themed Record of Lodoss War and with both of them inspiring the styles of Escaflowne and other classics of the 90's. While there had been plenty of low fantasy before Ys, mostly drawing inspiration from either Japan or the Middle East in the case of Tezuka, Ys puts itself out there with swords, villages, prophecies of chosen youths, goddesses and lores of old, and exactly the sort of visual style we'd expect from a story following in the footsteps of Lord of the Rings and its ilk.
Barring my dislike of the genre, my honest assessment of Ys is that fans of high fantasy are exactly the people who will enjoy it. There's nothing fancy, but there's also nothing wrong or unappealing. For those wary in light of the recent Hobbit trilogy, Ys is a tight package, with each of the seven original episodes handling a different dungeon as it were, complete with a boss, story, weapon upgrades, and the like. It begins with the chosen youth Adol Christin finding his way to the lost shores of Esteria, the former kingdom of Ys, and ends with him fighting the sorcerer Dark Fact to return peace to the land, and in between is a straightforward but appropriately “epic” coming of age. If that's not your thing, like it isn't mine, then there's no real point; if it is your thing, Ys is both a worthwhile little tale and a neat history lesson in the origin of the genre in anime.
The second season is a bit of a different story. The first OVA gives Adol seven episodes to find six ancient books, with a clear boundary between the forces of good in the towns and evil outside the walls, so the pacing of each episode (and the show as a whole) is laid out in advance. The sequel Ys II: Castle in the Heavens is four episodes, and besides the simple goal of removing evil from the world there isn't a clear progression out in clear sight. Even the setting is a bit of a mystery. The kingdom is clearly Ys, and the same Adol from Ys comes to rid the kingdom of a similar evil, but we don't even know when in its history he's been transported to; no prophecy, no knowledge of the ancient texts, nothing. And his attempts to resist the false peace and exploitation of the common folk is met with hostility even from those he tries to free, more ignorant and scared of retribution than seeking to escape the status quo.
I would say even for those not interested in the seven-episode tale of Ys based on my disclaimer from before, Castle in the Heavens is worth the time. It tests the boundaries and morality of the world while also touching up the visuals and fight sequences, and also skirts around the hint of harem building the first season had. In the first, we meet Adol through his quest to find Esteria before we actually learn about the world, and so we're led to follow his character as he matures into his role as a hero. In the second, we relearn the world from scratch, and only after—or even incidentally—do we remeet the Adol who is meant to save it. The former works in the context of the genre, because D&D teaches us to grow as that hero, while the latter works because the world has an appropriate sense of despair, and a clear need to be saved.