I found Vala to be kind of annoyingly over the top. And Browder a little wooden.
But the bigger problem with the last two seasons of SG1 to me was that the Ori were too powerful to be interesting. You couldn't bring them down with the same cool ground battles and pyrotechnics we got early in the series. You needed to discover an ancient deus ex machina. But I guess that wasn't a new problem with the series, it'd been a problem since Anubis.
Browder wooden? I'm sorry to hear that

The Ori were a mixed bag for me. On the one hand, you had an all powerful force that couldn't be reasoned with that forced Earth to join forces with Ba'al for a while in order to survive. I thought that was interesting.
Though, I agree the deus ex machina solutions were getting a bit tiring, but then that had been around since, what, Season 2, or possibly even Season 1.
As I understand it, the Ark of Truth was basically a condensed version of the original plans for Season 11. They would have spent the season searching for the Ark and used it at the end to defeat the Ori.
Ark of Truth could have worked better if they focused more on that and not other, less relevant plot points.