Excellent question. Here's my extremely long and detailed answer which covers the history of the Dalai Lamas and their behavior. You can also find my response on a description of the Tibetan system of slavery here, which is of course, extremely easy to confuse with feudalism. Neither slavery nor feudalism as we understand it in the Western world is really an accurate term to use for Pre-1950s Tibet.

For the behaviors of the Dalai Lamas themselves, to say nothing of Medieval societies in general, and Tibetan society in particular, I can say that few of them had any time to actually be cruel or commit what we would otherwise call "crimes against humanity" such as slavery or cruel and unusual punishment.

The First and Second Dalai Lamas held religious power similar to the earliest Popes, or maybe even some of the modern ones. Where their followers were perfectly free to follow them or not. These first Lamas did not have the power or stature as the later ones. They weren't (and aren't) even technically the heads of their own "Church." The Gelukpas are technically ruled by the Ganden Tripa, and the Panchen Lama is even considered (in some circles) equal or greater than the Dalai Lama's own spiritual powers. Historic forces propelled the Dalai Lama to prominence, however. The First and Second DLs were merely one Lama among a sea of many which most Tibetans were free to leave or follow.

The Third and Fourth were considered the patrons of Mongol khans, but were similar (though had a far shorter reach) than some Medieval Popes. The Khans were given religious instruction and promised to spread the Gelukpa school while the Lamas granted the Khans legitimacy.

The Fifth was the first to attain full temporal power, conquering Tibet in 1642 through Gushri Khan, a Mongol chieftain of the Qoshot tribe. However, when you read as many Tibetan history books as I do, you soon become skeptical of the Fifth's actual power. He seems almost entirely unaware of - for example - the conflict with Bhutan. It isn't mentioned once in his autobiography. The Desis - Regents - seemed to have more control over Tibet until the 1900s. The Sixth had almost no political power. The Seventh had some but was more interested in academic pursuits. The Eighth seemed to have some. But the Ninth through Twelfth never reached their majority.

The Thirteenth was the first Dalai Lama to have what we would understand in the modern West as "political power" and the First Dalai Lama who would be able to preside over Tibet with some authority to modernize it. That said, he made quite the effort to modernize his country and bring it past the (for lack of a better word) feudal phase. It was quite an effort, and unfortunately, he more or less failed (especially since he was occupied with various attacks from Russia, Britain, and China, and worked very hard to try and get international recognition for Tibet... he failed).

As u/Thecna2 said, the current Dalai Lama fled Tibet when he was 22 or so. He was only 13 when the Chinese first invaded in 1950. So hardly had time to engage in a lot of cruelty. Especially since the Chinese were breathing down his neck nearly the entire time he was in the Potala, doing their best to dismantle Tibet's society (under the guise of modernizing their feudalism).

For further reading and to draw your own conclusions, Tsering Shakya's Dragon in the Land of Snows for the history of modern Tibet. As for ancient Tibet, so far I think Alexander Norman's The Secret Lives of the Dalai Lama is the most unbiased source. Keep in mind that the primary sources used to gauge Tibet are hardly unbiased themselves. The truth is that we may never know much about Ancient or Medieval Tibet except for what those ancient monks tell us. The other option - to believe what the Chinese say - is hardly unbiased. As far as Michael Parenti, I just can't believe him. It's basically the opposite extreme from kissing Dharamsala's ass... and that would be kissing Beijing's.

One day Tibet may be open and archaeologists might be able to piece together what the last 2,000 years were like in Tibet with more detail, but I'm guessing that until then, we'll be fed one story from Beijing, another from Dharamsala, and we'll have to just walk a middle path.

I assume you mean the current Dalai Lama, not how the Dalai Lamas worked overall ? If so its hard to refute or confirm something as vague as this. He was around 22 when he fled Tibet so he didnt get much time to be cruel. Tibet was a comparative primitive country at the time and may have functioned like what you'd expect a 'feudal' society to behave, compared to the west. I'm unaware of any specific 'cruelty' that occurred that wasnt a standard part of any society of that lowish level of sophistication during this period. I'd be interested in the source of these claims, especially if theyre chinese sources.