Look, I'm not saying the original magnificently hammy bastard that the Master always acted like was anything other than brilliant, but the John Simm Master was fantastic in his own way. He was exactly as arrogant and egotistical as his old incarnations, but the new regeneration gave him a sense of humour. And what do you get when you give an arrogant, egotistical bastard a sense of humour? Pretty much the way John Simm played him. I thought it was a brilliant take on the Master.
The Doctor is a classic Trickster archetype. No weapons, no aggression, and usually no idea what's going on, but he bumbles his way into the Apocalypse, fools the bad guys into blowing themselves up, shares a jelly baby or two with the survivors, and bumbles off again into the sunset. It's a big part of his charm and his character as well as why he's so good at what he does, because everyone always underestimates him.
John Simm was the Master who took on this trait: He was an evil Trickster. He cackled, laughed, sneered, and then
outwitted the Doctor. Multiple times. He defeated the Doctor, Captain Jack, and the entire world for entire year, only underestimating Martha. When he came back from the dead, he didn't even make that mistake - he tricked everyone into letting him copy himself onto every human in the world, and ultimately had the Doctor beaten until the returning Time Lords betrayed him. Say what you will about how you liked his portrayal, but he came closer to winning than any incarnation of the Master before him.
Basically after thirteen regenerations of learning that his Evil Grand Vizier archetype wasn't giving him victories, he stole the Doctor's greatest weapon by becoming a Trickster like him. He was just as hammy and smug and unmistakably evil as he's always been, but now he did it with a grin on his face and cackling with genuine delight as he watched the world burn around him.
You may not have liked it; but I loved it.