Then how do you feel about DA lore since the start of the franchise? When Origins begins, the very first thing we get is the Chantry's legend of how the darkspawn came to be, and over the course of the series we gradually got evidence that this turned out to be true. It makes sense that we'd finally get to meet some of these weirdos, and that at least one of them might want to try to finish what was started.
Well said, it's not like Corypheus' plan doesn't actually have some credibility to it either?
He has already broken into the Fade and entered into the Black City once before, the only problem last time was that something happened to turn him and the others into Darkspawn and either boot them from the Fade, or send them running back to their portal in terror, bringing the taint with them. What really is stopping him from trying again, and this time, trying to not make the same mistake?
The only real questionable part is his belief that taking control of the Black City will make him a God, which has never been proven.
Aside from that, his plan to break back into the Fade again, as well as the ways he attempts to do just that, actually comes across as well thought out?
His attempt to use the Breach and the Anchor fail because we stumbled in and stole it from him. He then launches an attack on Haven to attempt to get the Anchor back, but finds he can't. He then immediately switches to Plan B which was to try and use an Eluvian, which he's been having people searching for ever since the Breach, showing that he clearly had backup plans in case he failed.
It's only when we mess Plan B up, that he loses his cool completely and has his cosmic temper tantrum. The loss of his desired armies earlier in the game clearly annoyed him, but it's when we take victory from him once again that really pushes him off the deep end.
(Corypheus' only problem is that he often suffers from being a Badass On Paper. His plans are actually clever, but he doesn't act like it in person, so we can't take him seriously)