The Super Bowl is the biggest single day in advertising, with companies this year reportedly spending more than $5 million to run a spot. And with the low-scoring game turning into a bit of a snore-fest, the focus on the ads was perhaps more intense than ever.

This year's Super Bowl commercials were a "solid bunch of ads," but lacked the pizzazz of some of the all-time greats, like Apple's "1984" ad or Volkswagen's ad featuring a little boy dressed as Darth Vader, said Derek D. Rucker, professor of entrepreneurial studies in marketing at the Kellogg School of Management at Northwestern University. The Kellogg School reviews Super Bowl ads each year for marketing effectiveness, grading the ads on a scale from "A" to "F."

Top Super Bowl ads need to be more than funny or eye-catching to be considered successful from a marketing standpoint, Rucker said. The best spots combine a top-notch creative component -- like a flashy setting or a celebrity -- as well as a strategic element that conveys the brand's message in a compelling way to viewers.

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"You really want to know what a brand is hoping to accomplish," he said. "For some brands, it's to make sure my brand stays top of mind or that you are aware of a new product -- and then the goal is, 'Will I see an increase in sales?'"

Six ads earned an "A" this year, according to Kellogg's yardstick. Only one earned a failing grade -- Burger King's ad featuring the late artist Andy Warhol. These rankings don't always match up with USA Today's ranking of Super Bowl ads, which is based on consumer responses rather than marketers' assessment.

Best Super Bowl ads

Microsoft's "We All Win."



This commercial earned an "A" from Kellogg because of its distinctiveness and emotional depth. The message was about how Microsoft is developing tools to help everyone win, such as a gaming device that helps people with disabilities play with more ease. That helps consumers "understand the brand's DNA," Rucker said.

The Washington Post's "Democracy Dies in Darkness"



Another "A" for this compelling ad narrated by Tom Hanks and featuring journalists who have lost their lives, such as The Washington Post's Jamal Khashoggi. "We acquire and desire knowledge. That's something we want," Rucker said.

Expensify's "Expensify This"

The ad -- the first-ever television ad for this company -- used humor and flash to highlight the benefits of its service: providing an easy way to expense your receipts. "That ad didn't just entertain me -- it made it relevant," Rucker said.

Bumble's "Ball in her Court"

Featuring Serena Williams, this ad used emotion in a powerful way, Rucker said. Its message about empowering women was distinctive and tied back to the brand, he added.

Google's "100 Billion Words"



This spot showed people using Google to translate words and phrases and connect with people from other cultures. Said Rucker, "They have figured out how to interface their brand with their life and emotions. The ad used emotions in a powerful and positive way."

Amazon's "Not Everything Makes the Cut"

Amazon's second year in the Super Bowl again scored points. "They showed all these various amusing situations, with the idea of things they don't do well," Rucker said. "Then they showed everything they do do well, and it revealed why they are so good as a brand."

Worst Super Bowl ad

Burger King's #EatLikeAndy



The ad had a number of problems and was the only spot to earn an "F," Rucker said. First, it wasn't clear that it was an ad for Burger King, with some viewers thinking it was advertising Heinz ketchup, since artist Andy Warhol is shown struggling to get the ketchup out of a bottle.

"There's an expectation you will do something interesting and engaging, and it fails on those core fundamentals," Rucker says. "It's uninteresting, and there isn't strong brand positioning behind it."

It's also unclear how many viewers will recognize Andy Warhol, who died in 1987, which limits the appeal of the commercial.