The first time I went snowboarding, I bought a package that included 3 group lessons. I had a blast in the two that I did attend, and funnily enough for the reasons that were already mentioned in this thread.
The First lesson we had (group of about 7, 4 of which were my friends and I) was very good. This lesson was marked as "first time snowboarding." He took us to the "kid" slope (not the bunny slope, but the kid area where the "lift" is like a conveyor belt) and showed us how to make toeside and heelside turns/carves. He first described it, showed us, then had us do it one at a time and gave us feedback immediately. After a few times down we went to the bunny hill and worked on linking them. By the end of this lesson I had absolutely no fear of going down a green run. Its not that i didnt fall when i went down the run, just i wasnt like "oh shit im gonna die" mode. Our instructor for this lesson was a younger guy, about 19, and he looked like he was having fun instructing us, so it made it more enjoyable for the group.
The second lesson (marked as "comfortable on greens" difficulty), it was obvious after 10m into it that my friend and I were better than the rest of the group. This instructor (probably about late 20's female) took us to the bunny hill and tried to teach us "falling leaf" and "garlands" when we had been practicing linking turns by the end of the last lesson. After about 15m she got another instructor to take us up by ourselves on a blue run, which was a pretty long run. We spent the rest of the time going down the run twice, but each time we would go about 100-200ft, stop, talk about what we were working on/ what we need to do different, then he would he go ahead and wait for us to come down, or tell us to ride to a certain point so he could see us from behind.
Don't get me wrong either, the woman from beginning of the second lesson was a great person and instructor, she just had to teach to the level of the "weakest" link. As far as what i would say made the lessons good, was that they were attentive to the group, seemed like they were having fun teaching us, gave good feedback, showed you what to do as much as told you, and made the overall experience enjoyable.