It'll be a blood bath although I suspect for both sides. We called it FISH and CHIPS - fighting in someone's house and causing havoc in people's streets.*
No solider, and I mean no soldier, will look forward to that, and it'll be worse if the Russians cause mayhem by using or air or artillery on the area.
Every house, basement and crater becomes a fortress. You have restricted movement, lots of technology becomes redundant and vision is totally diminished.
For the defender, lots of every day items become weapons (petrol bombs, IEDS, booby traps), while they have great protection and vision including from above.
Logistics is even more of a nightmare than it usually is - the Russians will hate this - and debris will causes lots of casualties, which are harder to extract.
The first doctrine to FIBUA* fighting is to avoid it - and that's the actual official line! *The official terms is FIBUA or fighting in built-up areas.