I know of a few that I would rate higher.
....
Satyajit Ray's Apu Trilogy
Pather Panchali (1955)
Aparajito (1956)
Apur Sansar (1959)
Yasujiro Ozu's Noriko trilogy
Late Spring (1949)
Early Summer (1951)
Tokyo Story (1953)
Krzysztof Piesiewicz' Three Colors
Three Colors: Blue (1993)
Three Colors: White (1994)
Three Colors: Red (1994)
Linklater's Before trilogy
Before Sunrise (1995)
Before Sunset (2004)
Before Midnight (2013)
Park Chan-wook's Vengeance trilogy
Sympathy for Mr. Vengeance (2002)
Oldboy (2003)
Sympathy for Lady Vengeance (2005)
Wim Wenders' Road Trilogy
Alice in the Cities (1974)
The Wrong Move (1975)
Kings of the Road (1976)
Rainer Werner Fassbinder's BRD Trilogy
The Marriage of Maria Braun (1979)
Lola (1981)
Veronika Voss (1982)
Gus Van Sant's Death trilogy
Gerry (2002)
Elephant (2003)
Last Days (2005)
Aki Kaurismaki's Proletariat trilogy
Shadows in Paradise (1986)
Ariel (1988)
Match Factory Girl (1990)
Laura Poitras's post-9/11 America trilogy
My Country, My Country (2006)
The Oath (2010)
Citizenfour (2014)
Aki Kaurismäki's Leningrad Cowboy trilogy
Leningrad Cowboys Go America (1989)
Leningrad Cowboys Meet Moses (1994)
Total Balalaika Show (1994)
Alejandro González Iñárritu's Death trilogy
Amores perros (2000)
21 Grams (2003)
Babel (2006)
Aki Kaurismaki's Finland Trilogy
Drifting Clouds (1996)
The Man Without a Past (2002)
Lights in the Dusk (2006)