"Big 4" means Best Picture, Best Director, Best Actress, and Best Actor.
These are ranked by year.

In the notes, I list which Academy Awards it is, the year represented by the award, and the award won.

Note: The 5th Oscars had a tie for Best Actor.

I thought it would be interesting to see the years where there was no dominant Oscar-winning film. Interestingly, within the first 13 Oscars this happened 5 times, then it didn't happen until a little streak at the 24th, 25th, and 29th Oscars, then not again until the 78th, 85th, 86th, and 91st Oscars. The run of 48 straight Oscars where this didn't happen was mostly due to Best Picture and Best Director going together almost every year. I'm impressed by how diverse the Oscars have been recently, at least in these 4 main categories.

Here are the years ranked by average rating, highest to lowest (Oscar # - Year - Rating):
13 - 1940 - 3.91
91 - 2018 - 3.84
86 - 2013 - 3.83
24 - 1951 - 3.82
85 - 2012 - 3.68
78 - 2005 - 3.66
94 - 2021 - 3.64
25 - 1952 - 3.58
10 - 1937 - 3.53
5 - 1931/32 - 3.50
29 - 1956 - 3.45
4 - 1930/31 - 3.04
2 - 1928/29 - 2.71

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Status: Updated through the 2025 Oscars
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My "Oscars Combined" series:
Best Made: Films That Won Oscars For Cinematography, Production, and Editing
Critically Popular Films - Money, Awards, and Critical Acclaim
Films That Won Best Cinematography and Best Screenplay In the Same Year
Films That Won Both the Best Actress and Best Actor Oscars
Films That Won Both the Best Supporting Actress and Best Supporting Actor Oscars
Films That Won Oscars For Score, Sound Editing, and Sound Mixing In the Same Year
Years Where a Different Film Won Each Of the "Big 4" Oscars