I thought Inqusition had a lot of promise, but the narrative just took a nosedive in a similar way to how Mass Effect 3 did, everything was so focus on building up strenght for a final showdown, the "mystery" of what was going on was resolved fairly quickly and after that it was all about winning micro battles and gathering allies before facing the big bad...it all felt rather hollow and anti-climactic when you finally got to the resolution...it's like a Bethesda main quest...too big for it's own good.
I don't know how much Casey matters or what went on behind doors to make him leave, but hopefully they can realize the potential of their ME and DA universes cause they truly are stunningly rich in potential.