Dragon Age Origins and Dragon Age II happen at almost the same time and use some of the characters from the first, but pretty much a new cast and a new locale.
Dragon Age allows you to explore various environments and interact with a choice system that alters the course of the story. You can alter little things like the order you tackle story events to big things like who will stay and leave your party and who will be your allies at the end of the game.
The battle system in DA uses a macro system that allows you to make character rolls such as tank, healer ect... The combat isn't super fun and can be sluggish but the story and interaction makes up for it.
You can customize all armor and weapons for each character and enchant items to really deck out what you want. There are several paths to take so replay value is there.
Dragon Age II is getting lots of grief for being to mainstream and repetitive dungeon layout, DAO doesn't have that problem though. DAO and DAOA are both good games to play.