To jump back a post, there were two major problems for this season: lack of time and lack of material.
The showrunners are ahead of the books and now we can see just how reliant they were on Martin's writing. The scripts flattened out noticeably, without the clever twists and turns provided by the author. Knowing the major plot points that Martin is planning (which I've heard that he communicated to them) is not the same as telling a story. The devil is in the details. The showrunners were excellent at summarizing the best parts of the books, paring away details but retaining essential turning points, but not so good at coming up with that depth on their own. It's an entirely different skill set or talent, and they didn't transition gracefully.
Meanwhile, since you haven't seen the series, your arguments about Cersei are weakened by a lack of knowledge of where she's been and who she is. Cersei has been implacably villainous, yet she reached a point a few seasons back that actually won that sympathy from viewers. And she did it with incredible backbone. Her Walk of Shame is an iconic event in the series, and despite all her despicable deeds, it was impossible not to be moved by the attempts to break her spirit and her ability to maintain her dignity in the face of screaming mobs -- naked, vulnerable, but unbowed.
Having seen her emerge from that crucible even more hardened than before (which is saying a great deal), the final scenes of her life in Episode 5 just don't ring true. And the whole pregnancy thing was... weird. Given the time that passed since she first announced her pregnancy, she should have been the size of a blimp by the time she died. I still wonder if the pregnancy was another of Cersei's tricks, but the showrunners forgot to let the audience in on her subterfuge.
And finally, having a sword fight between Dany and Cersei... no offensive, but that's kinda ridiculous. Dany has a dragon. You don't jump off the dragon to kill your enemy, you just roast them on the spot.
= new reply since forum marked as read