What are the biggest challenges to Russia's economy?

Petro-dependency, corruption and stagnation, I'd say

Russia is topmost in oil reserves. Good enough in industrialization and infrastructure.

Russia is one of very few countries free of debts. people do not mind austerity.

They have shown the spirit in WWII.

Russia has been a poor country under Romanovs.

communism brought Russia out of marshes.

But, West made the rulers enter into competition with USA in nukes and shuttles.

They lost almost everything they gained.... and then people abandoned communism.

I think the problems after 20 years are

Around the same time derivatives caught the world and fake growth started, which was an impossible charade for a new democracy.

Russians still confused about " nature and enquiry into nation's wealth".

Russia is viewed upon as unwelcome partner in capitalism by the west because they maintain they have not surrendered.

But,

I do not think they need any adaption of attitude because the "ideal" system is falling down rapidly.