The first Standard results with Core Set 2019 are in and Nicol Bolas is ravaging the format!
What makes Nicol Bolas so good?
Making comparisons to four-drop mythics like Hazoret the Fervent, Rekindling Phoenix, and Chandra, Torch of Defiance is a reasonable place to start when trying to evaluate Nicol Bolas. On its face, Nicol Bolas doesn't seem to stack up to those cards, especially considering how the other cards have been riding roughshod through Standard for quite some time now. I mean, it's a three-color card.
Evaluating Nicol Bolas comes with a lesson of context. If the entire format is playing cards like Vraska's Contempt and Hour of Glory to answer Rekindling Phoenix and Hazoret the Fervent, Nicol Bolas is much more appealing (assuming you ignore the somewhat prohibitive mana cost).
The other thing that sets Nicol Bolas apart from the rest is the fact that if he lives, you will eventually win the game. In the first league I played, I transformed him twice and had the opportunity to do it two other times, but my alternate options were stronger. Transforming Nicol Bolas is very real, it comes up often enough (and more so in the versions with Liliana, Death's Majesty I'd imagine), and when it happens, you typically win.