What was special about the 2021 Formula 1 World Championship?

The 2021 Formula 1 World Championship came down to the final race of the 2021 season in Abu Dhabi.  Seven-time world champion, Lewis Hamilton and Max Versteppen were tied in drivers' points, with this race being the deciding factor of who would be crowned champion. 
Ultimately, the 2021 Formula 1 World Championship was won by Dutch driver, Max Verstappen.  This was his first Driver's Championship title.  

What makes this particular championship special, or controversial (depending on who you ask), is that the race director, Michael Masi, misinterpreted the regulations regarding a late safety car restart.  Masi called the safety car back into the pit lane without it having completed an additional lap as required by the Formula 1 Sporting Regulations (Article 48.12).  By not heeding these regulations, all lapped cars were not able to unlap themselves which resulted in Max Verstappen being in a position to easily overtake Lewis Hamilton for the win.