Also, how much of their infrastructure was built in Soviet days, and how much of it remains today?
It definitely depends on which country you are referring to considering how different things were in somewhere like Ukraine for instance, which joined the USSR in 1922, compared to other nations like Hungary which had a bit more homegrown Communist Party that had been around for decades when they adopted communism after WWII.
If we're strictly talking about average life quality I would say communism did improve average quality of life early in the USSR under Lenin's agrarian reforms because the peasantry was given more of an opportunity to close the gap with the rich nobility of Imperial Russia. Thay said, there were of course many people who did not benefit from the establishment of communism in Russia, namely the Cossacks, Ukrainians, the Baltics, the rich, and religious institutions.
Outside of Russia, most European nations who adopted communism did so while Stalin was still basically running the Cominform which he essentially saw as a way to govern the leaders of the other nations, who he hand-picked to go in line with his wishes (they're even called mini-Stalins). Stalin stressed the importance of heavy industry rather than agriculture so while the nations were mostly able to modernize (Romania was responsible for producing much of the agricultural products for the entire Bloc so they didn't really modernize their industry arguably until later under Nikolae Ceausescu)**, each one was responsible for producing oddly specific products (Hungary was responsible for producing busses for example). This meant that most people were just stuck in these jobs without much incentive to work hard. In that sense, their lives did not improve, but at the same time many historians would argue that the form of government the Bloc nations adopted in the 1940s was an extreme perversion of communism.
Yugoslavia on the other hand had a dramatic improvement in their quality of living once Josip Broz Tito emerged from WWII after fighting the Nazis, Italians, and a civil war all at the same time. Tito managed to roughly unite the various ethnic groups of Yugoslavia for a time despite them really having no historic basis to be united.
I can go into more detail about specific countries if you'd like (except Albania. I really don't know enough to speak confidently about it) but I just wanted to try and cover most of Eastern Europe as broadly as I could here. It's pretty common to lump Czechoslovakia, Hungary, Poland, Romania, Bulgaria, and the GDR under the blanket term of "satillites" but they are actually very unique.
**/u/adagencies - "Gheorghiu Dej was a staunch Stalinist who was very, very focused on industrialization." Not sure what I was thinking, thanks for the correction.
A little yes but more no.
One thing that came with the fall of the old regime is that some of the old laws where not enforced anymore. The Communist under lenin had some good (modern) laws regarding womans rights and such. Go over to /r/socialism and you can let them tell you how great everything was. There was quite a lot going on in art and such as well, people where inspired by the new (sadly short lived) 'freedom'.
Im not well versed in social history so maybe some expert can add on some thing to this point, I have focused far more on economics.
Ok, so lets talk economiclly. First one has to understand that befor Lenin (and party) got power, most of the communist revolutionarys did not give to much thought on how this is all going to work. The few people (mostly http://en.wikipedia.org/wiki/Nikolai_Bukharin) who did think about these things had a sort of vision where everything was centrally controlled and guided and then distributed (see http://en.wikipedia.org/wiki/Planned_economy).
So when the communist came into power they where very quick about centralising everything. All big buissnesses like banks fell under party control. There vision was basiclly that the farmers would bring in the food, they would invest in all bug buissness and thanks to that the would completly outgrow the capitalists. This is nowdays called War Communism because there was a civial war going on, but really its a bad name because it didnt have anything to do with the war, it was there vision (http://en.wikipedia.org/wiki/War_communism).
Now in reality, this system produced some of the worst results imaganble. The farmers did not really feel like giving up all there food for as far as they could see no benefit to them (see http://en.wikipedia.org/wiki/Prodrazvyorstka), the collection teams where attacked, mass starvation and other problems. By 1922 even the communist elite noticed that they could not keep going like this and in a matter of a couple monthes threw together a new system, called the NEP (http://en.wikipedia.org/wiki/New_Economic_Policy).
Now the NEP restored many things as the where befor, the farmers started to bring in food again and where alowed to sell it. Buissnessman where alowed to own smaller buissness, the ruissian term for these people is Nepman (http://en.wikipedia.org/wiki/NEPman). Now ruissans of the time made jokes that implied, basiclly everything is as it was befor the revolution and the war. You had farmers selling, a small middle class of buissness owners getting richer and a groupe of people that controlled most heavy industry.
The real problem with NEP was that it did not serve the socialist vision very well, it was a system thrown together in order to survive, not to thrive. There was a great amount of disapointment with it, everything is as it was. Lots of workers and socialists where not happy, this is not what the imagend when the socialist revolution was proclaimed. Now eventually stalin managed to capitlaised on this but thats out of scope for this question.
So 1917-1922 bad, then 1922-1928 not to bad, some more social freedoms and simular to pre war economicly but then you get stalin after that.
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Also, how much of their infrastructure was built in Soviet days, and how much of it remains today?
I dont know, sorry.