From a US perspective: Omaha, Houston, Fort Worth, Lincoln Park, Fresno, Cheyenne Mountain and Nashville have all seen tremendous improvement over the last decade. The amount of investment that these seven facilities have seen over a 10 years period is extraordinary.
Follow-up: To emphasize how these zoos in particular have drastically improved in recent years, here's a complete timeline of developments from over the last decade or so for each of them, plus some projects for the imminent future. I didn't do the math myself, but this has to be somewhere north of a billion US dollars in upgrades between them all.
Omaha
2016: African Grasslands, Alaskan Adventures Waterpark
2017: Children's Adventure Trails
2018: Asian Highlands Phase I
2019: Asian Highlands Phase II, Glacier Bay Landing Plaza
2020: Sea Lion Shores
2021: Gorilla Valley Renovation, Simmons Aviary Renovation, Stingray Pavilion, Event Center
2022: Desert Dome Plaza
2024: Orangutan Forest
Houston
2017: Bull Elephant Yard Expansion
2018: Black Bear Exhibit Renovation
2019: Texas Wetlands
2020: South American Pantanal, Orangutan Exhibit Renovation
2021: Renovated Main Entrance and Plaza
2023: Galapagos Islands
2024: Birds of the World
2025: Jack's Cafe
Fort Worth
2018: African Savanna
2022: Elephant Springs
2023: Predators of Africa & Asia
2026: Jungles & Forests of the World
Lincoln Park
2015: Macaque Forest
2016: Arctic Tundra, Penguin Cove, Renovated Seal Pool
2017: Learning Center
2018: New Entrance & Visitor Center
2021: Lion House Renovation
Fresno
2012: Sea Lion Cove
2015: African Adventure
2019: Warthog Exhibit
2023: Kingdoms of Asia
2024: Conservation Action Center
Cheyenne Mountain
2013: Encounter Africa
2020: Water's Edge: Africa
2021: Demolition of Monkey Pavilion
2025(?): Great Ape Exhibits
Nashville
2016: Entry Village
2017: Mexican Spider Monkey Exhibit
2018: Expedition Peru: Trek of the Andean Bear
2019: Tiger Crossroads, Veterinary Center
2023: Komodo Dragon Exhibit
2024: Leopard Forest
2025+: African River Safari (multiple phases)