Getting verifiable information about this war is almost impossible.
My impression is that the most important factor so far has been USA truck launched long range missile artillery.
The Ukrainians can fire a 500 pound warhead up to 140 miles and strike within a five foot radius of accuracy. The missile artillery is very hard to shoot down, and the missile trucks are moving to a new location within 60 seconds of launch, which means return fire is almost impossible.
Bottom Line - the Russians cannot concentrate their troops or their equipment because of missile artillery, which means they have almost no offensive capability.
Does anyone else have this same impression, or are there other factors at work?
HIMARs is probably the most important factor in Ukraine's stunning successes. However, other high-tech weaponry get some of the credit.
The Ukrainians used Turkish drones to kill a lot of tanks preventing breakouts and pincers early in the war.
The Ukrainians also used commercial "copter" drones to kill a lot of tanks, APCs, artillery, and other military hardware.
The Ukrainians have used HARMs to negate or destroy the Russian short range/mobile surface-to-air threat.
MANPADs have shot down numerous helicopters and low flying fighter aircraft.
Javelin anti-tank missiles have provided Ukrainian infantry the ability to kill tanks and other armored vehicles during close-in fighting.
Ukrainians have also received night vision equipment. Here's a video of a Night Sniper Shot:
All of these high-tech weapons have been used to great effect.
Also, the Ukrainian's will to fight for freedom and their country is an important factor.