I was hoping for a couple things:
1. I wish they had told Todd about Lydia being poisoned with the ricin before they killed him. He deserved to burn first for killing the kid at the train tracks. I think it would have played out better like this: they go to kill Walt and drag him off before he grabs his keys, so he knows he has to come up with something quickly, so he tells them their meth supply from Lydia is going to run short soon. Then they throw him back against the pool table (giving him a chance to grab the remote control) and tell him to explain - then Todd realizes the full extent of what Walt has done. I think that was a big missed opportunity & would have been a lot more satisfying.
2. I wish they had more back story on Gray Matter. I wanted a stronger reason for Walt to hate them, like maybe Gretchen cheated on him with Elliott, which is the real reason he sold his share - he couldn't stand to be around them anymore, then they used his research to make billions. That would have given more weight as to why he would have them live in fear of the "hitmen" in the last season, because it doesn't seem like money would have been a strong enough motivator for him to care.
There's not much else I can think of to criticize. They tied up every other loose end I can think of. I knew as soon as they killed Hank, the show wasn't going to end well. I was hoping Hank was wearing a bulletproof vest and that Walter would escape, fake his own death, and become a drug kingpin in Europe, while leaving his family out of the DEA spotlight & free to live their lives thinking he was dead. But he had too much to answer for...Jane, the airplane passengers, Gale, Drew, etc. Plus I'm still mad at him taking out Mike, haha.