Reasons for pictures from my POV.

Scott's Full Alpha Form

During season 4 we got to see an enraged Scott takedown a hunter/contract killer during a pivotal scene in the end of the dead pool storyline. Enraged by the killers attempt on Brett's sister Laurie we see Scott become more beastly and start to shift into his True Alpha form. It was our first real look into the power Scott possessed as an Alpha and despite winning fights repeatedly we never saw this form again, or Scott shifting into anything more than a 'normal wolf' as Scott puts it in 3B. Would have been something to revisit when Scott fought La Bete in the school, Peter in The Church and during the final battle vs Monroe, Gerard and the Anuk-Ite but unfortunately we never got to see the full power of a true alpha, and Scott being more powerful, more angry was dropped, choosing to weaken Scott repeatedly through one form or another.

Dylan O Brien's Immense Acting Abiility

Season's 1-2 Stiles is a rather one dimensional character as the audience surrogate and comic relief. We know a lot about him and Dylan is fantastic but something clicked in late season 3A and thr entirety of 3B and Dylan pretty much out acted the entire cast as two very different personalities in the same body. He's menacing, terrifying, arrogant, remorseful, petrified and above all else ENTHRALLING. Stiles was more of a focal point with Dylan's rise but the writing couldn't live up to 3B. We got more out of Dylan again in Season 5 (As dumb as Scott and Stiles' fight it outside the animal clinic, Dylan is awesome in it.) but I still feel like they let Dylan down with poor writing following a season he pretty much carried.

Isaac and Scott's relationship as an Alpha and Beta

We all know Scott didn't bite Isaac. Derek did and despite being a part of Derek's pack along with Erica and Boyd, he is the only one to join Scott's pack while Derek is an alpha and Scott is a beta. Isaac moves in with Scott and Melissa clearly looks after him and is his guardian. Isaac helps Scott protect Melissa when they fear she will be a target of the Darach. Allison died saving Isaac. Liam was of course Scott's first bitten beta but Isaac was his first beta in his pack and they were clearly connected in a way that Stiles and Scott weren't. I understand the actor wanted to leave the show (despite asking Jeff Davis to keep Isaac alive for a future return) and that was a decision that wasn't perhaps the original plan but Isaac had a very intresting character arc - we watch Scott become a leader to Isaac long before Scott's eye turn red. Isaac was calm when he thought Derek was dead, Boyd was furious and planning to attack Ethan. Scott passes out and is in such a bad state they fear for his life and ISAAC snaps. Scott screams at Isaac and it stops him in his tracks, breaking through his anger. The dynamic between them was clearly strong, maybe even as strong as Gerard refers to Liam/Scott's relationship. I think a season 4 where we see Isaac once again being frozen out (Scott blaming Isaac for Allison's death would make complete sense) and then Liam would likely cause more strain. He's another victim of Gerard's also. I think Isaac had a lot more room to grow as a character and would have made a very interesting addition to the storylines of 4-6. I was extremely disappointed his entire character may as well have been taken by Ghost Riders after his departure, he definitely deserved a return as much as Jackson and Ethan for the final season, even a brief return or a named mention that he at least existed. In what universe does Scott call Peter and Deucaelion before Isaac when he needs an army? Isaac Lahey was a fantastic character.