Well, any games without an ending can be considered long games, but most don't have any story to speak of.
You could always try some of these, however:
2) Kingdom Hearts: 358/2 Days - It's a Kingdom Hearts game on the DS that stars Roxas. What's not to like? It's got a good deal of things to do and will last you more than 12 hours unless you decide to cheat. There's also an unlockable mission mode where you can play as other members of Organization XIII. Only problem: Hands are stuck straight, even when holding things. If you haven't played any other Kingdom Hearts games, then this will spoil a lot of that for you.
3) Kingdom Hearts Re: Coded - It's a redux of the original Kingdom Hearts. Instead of it being just a full on remake of the original game, however, it's got a new story. There are some new gameplay elements, such as side-scrolling platformer sections and some RPG (as in, the Mario and Luigi kind) sections as well. The graphics look much improved over 358/2 Days, as well, which is a plus if those darn hands bothered you. If you haven't played any other Kingdom Hearts games, this MAY spoil some things.
5) Final Fantasy: The 4 Heroes of Light - A throwback to the classic Final Fantasy games of yesteryear. The game's story HAS been called out on for being partially nonexistant/stereotypical, but that doesn't detract from the game at all. The gameplay has also been scrutinized over being a bit random, as the AI will choose which enemy to attack / friend to use items on depending on what you do (i.e. if a character has a spear or a bow and you tell them to attack, they'll attack an enemy in the back row. If you have two low-health characters and someone uses heal, the character with lower health will be healed). However, there's a very nice balance to it all and it gets easy to use as you master the game.