While I'm a bit unfamiliar with your situation precisely -- I'm not exactly a scholar of contemporary Bulgaria and am totally unfamiliar with what factors might have influenced the views of your parents and grandparents -- I do think I can say that Ottoman rule in the Balkans was a mixed bag and very much depended on your social position and your religion (and of course, the all important "when" question, as Ottoman rule in the Balkans was not uniform over its 500 year history).

I think the best way to start this answer is by giving you a few things to consider regarding the nature of Ottoman rule in the Balkans which would have positively or negatively affected the general quality of life for certain populations:

Slavery -- This is as good a place as any to start, since you bring up the reference to "500 Years of Slavery". As has been detailed in a great many works on slavery in the Ottoman period (Including but not limited to the work of Bernard Lewis, Ehud Toledano, Eve Troutt Powell, etc.) was a variegated institution with different types of tasks assigned to different races/religions/etc. You might generally breakdown the type of slaves into two parts -- slaves that were part of one or the other slave market/trade that could be bought and sold in public squares in most urban centers for various types of domestic labor (including concubinage), and devşirme, or boy tributes, collected during times of warfare as a sort of tax from non-muslim (mostly Chrsitian) families who were then forcibly converted to Islam, trained as soldiers and/or bureaucrats/scribes by the Ottoman Palace in Istanbul. To the extent that Ottoman slavery existed in the Balkans, it was almost entirely of the latter variety. Ottoman laws generally protected its Christian subjects from being bought and sold on the slave market, and so if there were non-muslim slaves in the Balkans, they would be of either African or Circassian provenance, generally speaking. However, the vast majority of the devşirme tribute boys came from families living in Greece/Balkans, particularly during the earlier periods. The Ottoman war machine was very active in the Balkans from the early 15th through the 17th century, and through most of that time, tribute collections were frequent. Obviously, have your first born son torn away from your against your will is a horrible thing to have happen, and this did happen a lot, but it should be differentiated from other sorts of slavery because these boys often lead a rather charmed lifestyle since they were trained in the best schools in the whole empire and ended up with careers as elite Janissary soldiers, or high-level bureaucrats. Many of the greatest political and cultural figures of Ottoman history came through the devşirme system. Something to keep in mind.

Non-Muslim/Dhimmi living -- Ottoman laws, as I mentioned above, provided a number of legal protections for "People of the Book" or "dhimmis". While for most of Ottoman rule non-Muslims were decided second-class citizens, they were afforded the right to practice their own personal status laws (marriage, divorce, inheritance, etc.) according to their own religious persuasion. Now of course for Christian communities of the Balkans, the situation could have been better from a legal standpoint had the land been ruled by one of the contemporary Christian powers, but it certainly could have been worse. Additionally, for Jewish denizens of the Balkans, this was a clearly preferable situation to contemporary Christian rule, as many Jews fled Western Europe for the Ottoman provinces in the Balkans following the Spanish Inquisition in the 1490s.

Warfare -- For the first couple centuries of Ottoman rule, the Ottoman war machine was basically grinding back and forth through the Balkans to fight the Habsburgs, Wallachs, etc.. The near constant march of war surely took a toll on local economies, and most likely did not help quality of life in many Balkan areas, Bulgaria especially since almost any route to the north would go through that territory.

Nationalism -- this is probably the biggest influence on contemporary Balkan feelings about the Ottomans. Bulgaria's separation from the Ottoman Empire was surely an acrimonious and bloody one. Two wars in the course of 30 years (and one that ran pretty much right into WWI) were accompanied by a massive migration of Muslim subjects out of the Balkans, which amounted to some pretty cataclysmic social and demographic changes for the region as a whole, and certainly would have left some bad feeling between the budding nationalist groups towards the Ottomans (and by extension, the successor Turkish Republic).

That being said, it's not as if the Bulgarian hatred for Ottomans was all-consuming. In some of my own research I've looked at students of independent Bulgaria who attended Robert College in Istanbul during the late 19th and early 20th Century. The mere fact that elite families in an independent Balkan state would feel comfortable sending their kids back to the imperial capital for an education is one sign that while Bulgaria desired independence, many still felt an attraction to the imperial metropole. In addition, in some of these records, there are names of students who went on to be key figures in the early constitutional congresses and parliaments in Bulgaria. Likewise, during the run-up to the 1912 Balkan war, many Robert College students from participating nations were at the very least civil as they took classes side-by-side in Istanbul. I remember one student (I think he was Bulgarian) quoted in the records as having said of an Albanian student, "had we met in the wilderness in my home country, I might have been compelled to kill him, but here I am his schoolmate." or something to that effect.

I hope that helps clear a few things up. I think at the end of the day, the responsibility for that viewpoint lays with a Bulgarian nationalist education, but it's important to remember that it's not entirely untrue, but maybe more than a bit misleading.

Good or bad are grand epithets that take into account a small part of the whole.

From an economics perspective, the Ottoman rule, compared the the western monarchies was simply different. It had both bad and good sides. Most notably the slave/second/raya class, while technically serving the sultan and his representatives, was not regionally bound. Whereas the european pesantry which inherited the roman empire's slave system, owed fealty to their lords - among other things, like taxes in kind (percentage or portion of produced goods), they had restrictions on leaving the lord's land. This freedom allowed a small potion of raya people on the Balkans to engage in free enterprise - speculative trade and transportation of goods. This was extremely profitable, but also highly dangerous. On the other hand the entire Ottoman system was fueled by plunder, but as the advancement in Europe was halted, bribes became prominent. The officials allowed these enterpreneurs to operate. This not only filled their pockets at next to no risk, but it created the "chorbadjii" and a class system among the raya.

The problem about your question is that it takes a perod of over half a milenia and one of the most rapid and turbulent times of human history. There are large spans of peacefull co-existence and some uprisings ending in some of the bloodiest massacres ever recorded. Life in the Balkans during the Ottoman rule had periods of drastically lagging behind Europe and perods of rappid advancements. It really depends on the specific part of the Ottoman rule you're looking at. Taxes for example, would vary depending on the needs of the army and other factors. They'd range from on lower that those in Europe to now leaving enough products for basic survival. If fact this was the reason for some of the uprisings, including the April uprising, which was also forced by a tax increase. As far as the slavery - there were no slave markets, however there was a clear dicrimination between muslums and non-believers - raya. There were restrictions on owning weapons, punishments for a believer murdering a raya were not the same as the other way around. Technically there were freedoms, but they always had some restrictions - for example a church could not be built taller than a mosque. And then there's the entire government/legal aparatus which was extremely corrupt. Originally, in the early years of the empire, various forms of lordship were given to distinguished commanders, who however had little interest in ruling pesant farmers or playing judge/arbiter. Also there were many restriction on what these commanders earned and most of the money they'd get was supposed to go to the sulan/treasuty. The bribe came as a loophole, allowing these lords to benefit monetarily from the title. This encouraged them to improve their constituency, which in turn improved production. While economics in European countries was rapidly develouping and the vasalage system was declining, the Ottoman empire continued to cream the added value of the raya, putting pressure to increase output. This also expains the agriculturaly antiquated methods and virtually nonexistent industry on the Balkans on the eve of the 20th century.

In fact after the turn of the century and up until the end of WWII, Bulgaria and Turkey improved relations and trade by quite a lot. The problem came after the end of the war when Turkey ended up on the other side of the wall. The socialist government need an antagonist. Sadly the cource of the party was to treat bulgarian turks as second-hand sitizens, culminating the Revival Process during the 1980-s.