Storywise, in the west a story has a beginning, a middle and an ending. This is how that ancient Greek, Aristotle, defined a story. And that's why other ways of telling a story (also known as the narrative structure) seem unfamiliar to us, e.g. how movies from Bollywwod, India, are told. Or how the Japanese or Chinese or African tribes tell stories.
In both DA:O, DA2 as well as all three Mass Effect games, we had a beginning, a middle as well as an ending. We might not like how the story was presented, was told, or some characters were in the games, but the game still ended. We might not like the endings, but we'll still get one, an ending, I mean.
As for having a happy ending, some games need to have those, not all games need to have a happy ending. (or movies). I like movies, games or books with open endings where we as an audience need to think a little and maybe in our minds continue the story. I like a happy character as much as the next one, but where is the development possibilities there. (warning: small spoiler for Downtown Abby, and yes it is relevant here).
In the new season three of Downtown Abbey, there's a wedding which takes place; another wedding doesn't take place. The youngest sister do not get married. And why do I mention this?
Because this shapes her destiny, her future, and her deciseness in the months and years to come. The same can be said for Fenris, for Isabella, for Morrigan, and yes for Hawke herself.
To have experienced hope, love, betrayal, and to have overcome this is a sure sign of maturity, in life - as well as it is for characters in a video game.
I can understand why people need to relax and just nok think a lot when playing videogames. Migt I advice you then not to play Bioware's games? Today, there are a number of games out there, which lets you play, no, not without thinking, but will help you to relax after a hard day's work, e.g. Fate, Torchlight, and such games. I'm nearly 50 now, and if there's one thing I learned during my long life it is this: Everything in life needs to change, if it doesn't it'll either be doomed or consumed.