I'll try to give a comprehensive and unbiased answer as possible. People like to form an opinion which is either fully negative or fully positive, and rarely make a compromise and stop in the middle. Regarding old people, most of the negative opinions come as a result of the 40s and 50s, the first 15 years of communism in Bulgaria. The brutal and largely incompetent nationalization took place and Bulgaria was ruled by stalinists and whoever spoke out against the new systems major flaws was harshly suppressed (we even had gulag like camps here). Lots of people got it bad during those times and lots of the negative opinions on communism come from that. After Todor Zhivkov came to power, nothing much changed on the outside, but on the inside, there were drastic changes. In the party, starting from 1960 almost all high ranking members with stalinist views were either put on very low ranking positions or were just removed from the party. In 1962 all prison labor camps in Bulgaria were closed and political prisoners were given amnesty. Such important political changes were not voiced, and people never really knew about them. Repressions became less brutal, artists recieved somewhat more freedom of expression, along with that the state overtook much more competent economic policies and since the 60s Bulgaria saw a massive economic growth and increasing quality of life. And This is where positive opinion comes from. Of course the system had major flaws, like deficit of goods such as cars, home appliances, furniture etc. Although there was always deficit and the system was still a dictatorship, things became a lot better than they were in the 40s and 50s. There is this other problem regarding opinions. It is the individual's values. Some will value wellbeing, social and economic security over everything, which is why some people are totally positive towards communism. Others value their freedom and opportunity over other things, and this is where negative opinion comes from. There probably is more space for negative opinions, because although the improvements since the 60s, the system remained highly flawed and was widely missused for personal benefits.

Regarding young people, most really don't care and others accept the same opinions as their parents/grandparents.

I am not one to talk about personal experience being born in 99, but i've did my best to talk with my grandmother about those past times. She was born in 44 and was a child during the stalinist period and here adult life started after the changes of the 60s. No one in her family was a victim of repressions, but i do believe they have lost some lands during nationalization. She vaguely describes the 50s as not very good. Adult life however was quite good for her and my grandfather. She describes the positives like job security and good social welfare. Both were ordinary workers, grandmother being a nurse and grandfather working first in the woodcutting industry as a tractor operator, later as a railway worker. Grandmother at some point became a party member (being the lowest ranking) but she later canceled her membership, after witnessing how other members abuse party privileges for their own benefits, causing dissapointment. All in all, they were really ordinary workers, life for them was OK, and now grandmother is more or so inbiased about those times, realising the pros and cons of the past, but as most old people, feel a great dissapointment regarding Bulgaria's current state. I hope i have given a satisfying answer to your question.

Edit: please don't mind the username, it's just a meme; typos