The Ar Tonelico trilogy is an interesting little series of RPGs made by Gust, who are probably better known for their long-running Atelier series. The games have their share of flaws, but I find them endearing in large part due to the world building. The first two are on the PS2, and the third made the jump to 3D with some difficulty and landed on the PS3.
Some general things about the series. They all share a sort of post-apocalypse setting in which the surface of the planet has been covered by the "Sea of Death," a toxic and corrosive cloud layer. Humanity survives by living in and on a trio of colossal towers and the landmasses attached to them. Society is a sort of mix of medieval fantasy and high technology, and there's a nice sort of "lost technology" feel to a lot of things, including the towers themselves. Each game covers events at a different one of the towers.
The games have many themes of music and song woven into the plots, art style of everything from characters' outfits to buildings and enemies, and the setting itself. All magic is the responsibility of Reyvateils, women who can produce magical effects by forming their feelings into songs. ...Which all works by way of the songs being programs run on the Towers, requesting them to do certain things. There's everyday magic usually used in battle to attack, and also Hymns, which are much more obviously executable programs with specific aims and usually matter more for story purposes.
The first, Ar Tonelico: Melody of Elemia, covers events on the first tower, in which strange "virus" monsters appear from within the tower. The story follows Lyner Barsett, typical JRPG hero, in his quest to put a stop to the Virus threat. Along the way, he proves to be a prodigy with the game's crafting system, and meets a variety of friends, and so-on. The game also introduces pretty much all of the hallmarks of the series, including visual novel -like sections related to exploring the "Soulspace" within the minds of each of the three main Reyvateil heroines, really good music, and so-on.
The gameplay is very much "my first RPG" as far as the combat system goes. You have three front-line party members and one reyvateil in the back, because they can't do much more than concentrate on singing their magic. Song magic has some interesting mechanics in that it basically just keeps going as long as you have MP to sustain it. For some spells, this is a constant buff or other effect, but for attacks, they get stronger the longer they're charged (often far in excess of 100%). Battle is for the most part turn-based, but one can change song magic spells or activate attack magic that's charging at any time. Like every game in the series, it's a fairly easy game overall, and you can get through it with no intentional grinding.
The second game moves on to the second tower, and while it keeps pretty much all of the familiar elements of the first, it does have a much more interesting battle system. First off, you have two reyvatiels instead of one, and they work in tandem for song magic. Second, you only get two front-liners. Third and most interestingly, attacking is real-time, and basically runs as well as you can mash the buttons for each of your front-ling characters. It's similar to Valkyrie Profile in many ways. When it's on to the enemy turns, you have to defend your reyvateils by timing button presses to their attacks, and if you do well enough, you can negate all damage. It also gets easy by the endgame to just blow through most fights, but it's really fun to play, overall.
The characters this time around are also much more interesting. The protagonist is Croix Bartel, and he's refreshingly savvy and snarky, for a JRPG protagonist. The rest of the cast is also entertaining, and pretty much everyone who fights, does so with a crazy weapon. Croix uses a rocket-propelled lance that has a concealed machine gun. His little sister uses some sort of dual-bladed staff that converts to fancy hair clips for easy storage. His superior in the knights uses buzzsaw yo-yo shields, you pick up a lady who fights with a weapon that can be split into two swords, or combined into a bow or lyre, and so-on. It's just fun because it's all so ridiculous.
The third game...I haven't played yet, so I can't say much about it. I could probably drop a few things about the plot of all three games, but I'd rather not spoil too much for any of them.
So, world-building. As mentioned above, there's a lot about music, and the world in general is very pretty to look at and just an interesting and optimistic take, for what is also clearly post-apocalyptic in many ways. The people are happy, the mixture of technology, magic (which is technically also technology) and other medieval themes and weapons is fun to me, too. Most interestingly, they created their own language, Hymmnos, complete with its own grammar and alphabet, and use it liberally in the game's music, and otherwise. It's really interesting to see something that well thought-out for a couple RPGs. Someone really put effort into things, and I appreciate it.
The music, well, it's all phenomenal, particularly the major hymns from all three games. I'll likely link a sampling from all of them as the thread goes on. ...Which may be most of why I wanted to start one. I'll need to figure out how to do so most easily, though.