I'd bump DA2 to 6/10, considering they released it literally year and a half after first Dragon Age. The story was actually decent and it tied really well into Inquisition, that's pretty stellar for something they threw together in 18 months.
It definitely was the weakest link mostly because how small it was compared to grandeur of Origins and then Inquisition.
I just hope they won't fuck up DA4, it at the very least needs to be on par with Inquisition at which point I will be happy actually, Inquisition, after all, was super solid, great game and Trespasser also wrapped it nicely.