With Rosberg gone, a key factor this season — starting Sunday with the Australian Grand Prix — will be how three-time champion Hamilton gets on with his new teammate.
Valtteri Bottas was plucked from Williams after Rosberg's shock announcement. The calm Finnish driver is seen as the perfect foil for the tempestuous Hamilton, an outspoken driver not afraid to stand up to management.
A perfect match in theory, perhaps not in reality.
Hamilton and Rosberg had a tense relationship and openly feuded at times, forcing Mercedes management to intervene. Crucially, however, the quick and consistent Rosberg also brought the best out of Hamilton — forcing him to up his pace in qualifying and on race day.
Even though he lost the title, at times last year Hamilton's driving was the best of his career. Some credit for that must also go to Rosberg's relentless competitiveness.
Rosberg quit F1 with 23 wins, but the 27-year-old Bottas has never won a race at this level. He has only nine career podiums and never finished higher than fourth in the championship. If he does not challenge Hamilton in the same way that Rosberg did, then Hamilton's level might drop.
If so, Ferrari's Sebastian Vettel, a four-time F1 champion, and Red Bull pair Max Verstappen and Daniel Ricciardo will be poised to take advantage.
Vettel is desperate to bring the drivers' title back to Ferrari for the first time since Kimi Raikkonen, his current teammate, won it in 2007.
The 19-year-old Verstappen made history last year as the youngest driver to win a race — and the youngest to qualify on the front row. He has huge talent and is a fearless driver. Ricciardo also won a race last year and the 27-year-old Australian showed great speed.
Ferrari demonstrated in pre-season testing that it may finally have turned the corner after a hugely frustrating campaign where it slipped behind Red Bull, much to the exasperation of Vettel. Ferrari showed more pace than Mercedes in pre-season testing, although those gains should not be taken as outright proof since teams can hold something back. The real indicator will come on Saturday, during qualifying for the Australian GP.
"It is always hard to say who now has the better car, but it is very obvious that Ferrari is stronger than last year," Verstappen said. "Mercedes is always up there as well. I think that they are not showing their true potential."
Fans gambling over the last three years didn't need to look too far down their betting slips — it was almost always a case of which Mercedes driver would win.
But new rule changes may help bridge the gap this time.
Wider tires, greater aerodynamics, bigger fuel loads and increased downforce should make the heavy cars five seconds quicker per lap. The tires are 25 percent wider, have more grip and — crucially — are more durable, enabling drivers to push harder and limiting the cyclical pit stop strategy that made many races easy to call.
There is also much greater license to develop engines, although each driver remains restricted to four per season before incurring penalties.
This wholesale revamp is a welcome boost for the sport and especially its fans, who in recent times were crying out for entertainment. As well as Mercedes dominating everything, some races were almost processional, with far too much emphasis on fuel and tire strategy and little toe-to-toe driving. Overtaking was seen as a bonus, rather than a key part of a sport representing the pinnacle of quick racing.
This lack of excitement even prompted two-time world champion Fernando Alonso to make the remarkable statement that F1 was so boring it sent him to sleep — and that the sport should instead be paying fans to watch.
The general mood is far more upbeat now, with drivers expressing overwhelming enthusiasm for the new cars.
"It's so much faster in the corners," said Hamilton, who has often spoken about wanting a return to a more challenging form of racing. "The force you feel on your body and on your neck is much higher. I've got bruises and bumps where I've never really had them before."
Verstappen made a novel comparison.
"If you would put them next to each other, last year's would look like a toy car," the Dutchman said. "With the larger tires, there isn't that much (to) spare. In certain corners you need to take a different line, or else you'll hit the curbstones."
Drivers will need to pile on muscle to handle these new, aggressive machines and have been beefing up in pre-season, rather than slimming down.
The rule changes even seem to have appeased Vettel, which takes some doing.
"It works pretty much like an aspirin, it fixes pretty much everything," Vettel said. "From a driver's point of view it's better everywhere. Braking is better, cornering is better, you've got more grip."
More competition and more excitement will be music to the ears of F1's new American owners Liberty Media. The Americans completed their takeover in January — ending 86-year-old Bernie Ecclestone's 40-year reign as F1's chief executive. He made way for Chase Carey.
With future plans promising to win back even more fans via an increased emphasis on digital media, it very much feels like a new dawn for F1. But what fans want most of all is an open contest on the track, like in 2010 when several drivers were in title contention in the final race.
Other factors should also work toward this.
One of those is limiting clutch control and radio communications, thus reducing the amount of help a driver can get. It's up to the driver to perfect his clutch settings this season, without outside help from engineers, hopefully making race starts and the dash for the first corner more unpredictable.
Fans will see some new faces, too, with 18-year-old Canadian Lance Stroll driving for Williams and Belgian driver Stoffel Vandoorne replacing Jenson Button at McLaren.
Better rules, faster cars, new drivers and fresh challenges: the F1 season is the most promising it has been for a long time.