Lewis Hamilton won his third drivers' world title in virtually untouchable fashion in 2015, but in a year of pressures and problems both he and his Mercedes team ended the season looking anxiously at their rivals.
The 30-year-old Briton, who lost his focus and his dominant speed in the closing three races to his team-mate Nico Rosberg, won the championship with a month to spare.
His complete supremacy for most of the season left him ecstatic, and then vulnerable, when a period of intense celebrations saw Rosberg take over as F1's winner as the champion lost his way and, at times, his composure.
Their in-team competitive relationship was the focus of much attention and merited a warning from Mercedes racing chief Toto Wolff, who said that if they "crossed the line" in their sometime squabbles it could result in dismissals.
Sebastian Vettel's Impact
Both men agreed that their in-team rivalry was essential for them to maintain their own form and edge and, at the same time, drive Mercedes forward as the much-improved Ferrari team, boosted by their arrival of four-time champion Sebastian Vettel, showed signs of closing the gap.
"I hope that Toto always comes back to the conclusion that it's actually good the way it is," said Rosberg.
"I can see a couple of extra grey hairs that have arrived. Maybe those are courtesy of us..."
Vettel's impact with Ferrari proved that Mercedes have every reason to be concerned as he reeled off three wins and 13 podium finishes to suggest the Italian squad can make 2016 much less comfortable for Hamilton, assuming he can rediscover his mojo, and Mercedes.
Max Verstappen - The Next Big Thing
Under new management, the scarlet scuderia improved throughout the year and, if early speculation can be believed, may try to recruit the year's outstanding newcomer Dutch teenager Max Verstappen of Toro Rosso to partner Vettel in 2017.
Kimi Raikkonen, who endured a topsy-turvy year, kept his seat for another season, but knows that the 18-year-old new boy has a talent way beyond his years.
He proved it with a series of stirring drives that contributed to him winning three awards at the International Motoring Federation (FIA) prize-giving gala this month - for 'personality of the year', 'rookie of the year' and 'action of the year', which was for his passing move around the outside of Felipe Nasr of Sauber at the high-speed Blanchimont corner during the Belgian Grand Prix.
"It's nice to win that because I really enjoy overtaking," said the big-grinning Dutchman, his arrival in F1 having given the sport a lift it needed as talk of buyouts, walkouts and financial problems swirled around throughout the year.
Renault Takes Over Lotus
It was no surprise, after months of court appearances and persistent trouble with unpaid bills, when Lotus confirmed their takeover by Renault for next year.
It was more unexpected that Red Bull chose to continue with Renault as their engine supplier, albeit with them badged by Tag-Heuer, given the way in their relationship had collapsed as the former champions blamed the French company for their loss of power and success.
The biggest shock, however, belonged to McLaren whose reunion with Honda, as engine suppliers, produced a year of failures and frustration that two-time champion Fernando Alonso and 2009 champion Jenson Button endured with wry humour.
They needed it. Passed easily by almost every other team, the once proud champion team McLaren were unrecognisable as a serious force.