Listed below are all the differences between the present and the post-invasion future (shown in the year 2036) seen throughout Fringe, arranged by episode and with pictures and timestamps wherever appropriate.
S4E19 - Letters of Transit
"They came from the future. At first, they only watched. Arriving at key moments in human history. We called them Observers. But in 2015 they stopped watching... and seized control. Citizen uprisings proved bloody and futile. Those who survived became known as 'Natives.' In an attempt to show their allegiance, some Native factions became 'Loyalists' and were marked by the Observers. The original Fringe Team fought the invasion, but was quickly defeated. Fringe Division was allowed to continue at a reduced capacity, but only to police the Natives. The resistance was quickly overcome... or so they thought."
The Observers enforced a curfew to make Natives go to their homes.
Walter, Astrid, and Peter were ambered in the lab. (Image 1)
They eat 'coffee chews' instead of drinking coffee. (Image 2)
The fate of the original Fringe team was a myth/legend. Simon: "The original Fringe team didn't vanish, they aren't missing, they died 20 years ago. They aren't coming back to save us from the Observers, they aren't in a desert, or Peru, or immortal."
Walter ambered himself on purpose. (Image 3)
Central Park was almost completely destroyed. (Image 4)
The Observer invasion in 2015 was also known as 'The Purge'.
The Brooklyn Bridge was destroyed. (Image 5)
S5E01 - Transilience Thought Unifier Model-11
They ate egg sticks. (Image 1)
Observers paved over Central Park and filled it with machines that pump carbon monoxide into the atmosphere. There's one such zone on every continent. They need less oxygen-rich environments. (Image 2)
A handful of walnuts was worth roughly $3000. (Image 3)
S5E02 - In Absentia
Harvard was taken over by Observers.
S5E03 - The Recordist
They ate chewable apple tablets instead of fresh apples. (Image 1)
S5E08 - The Human Kind
There were 'Truth Churches' where Natives could meet Observers without fear of being read.
S5E12 - Liberty
The Statue of Liberty had been torn down and the Observers used Liberty Island as a detention facility. (Image 1)
The Observers had not invaded the Redverse. (Image 2)