This really wasn't a bad ending at all. It actually makes a lot of sense. You can joke all you want with lolking, but the Lich King was bad ass and the best final boss in the game. For there to always be a Lich King makes a lot of sense, they even say so in the scene; the Scourge need to be controlled. For Bolvar to sacrifice himself and telling them no one can know is a very powerful ending.
If we are talking about the worst ending to a game ever, there's no game that even comes close to ME3. You can say it's all about the journey and not the destination, but when I spend 120 hours with these characters, I wanna know that they have a happy ending. Of course, I am still convinced Shepard was infact being indoctrinated and that choosing the Destroy option is the only way to break the indoctrination attempt. Hence the scene afterwards where Shepard appears to be back on Earth, but that has been talked about plenty in the Mass Effect 3 thread.