I wanted to know what modern day citizens of former-Soviet states think about USSR.
Many different ideas. This is our past and it is not so simple so there is no way to express everything in one sentence. Be more specific if you want exact answers.

Also, what they feel about Stalin today.
Again many different ideas.

I think it will be useful for you to understand that Stalin's USSR was very-very different from USSR-after-Stalin.

I think that now nobody wants to live in the Stalin's USSR and only some old people want to live in the USSR-after-Stalin.

Did they share the principle of unity against the West during cold war?
At the time of 1970s-1980s (last two decades of USSR which contemporary people still remember) the communist ideology in USSR was a kind of formality. And the "unity against the West" was more the object of irony than the "principle to share". People mostly did not care about it.