Honestly, my favorite aspect of the pack is having access to my teens throughout the day. Active high school only has 2 hours of classes out of a 7-hour school day. So for a player who tends to focus on their teen sims a lot, it's great to be able to go with them to high school (which we can custom-build like crazy) and, during those 5 hours they're not in class, work on relationships or skills or generally just develop them as characters. Graduating early is a nice option for similar reasons. Being able to go to university as a teen provides a nice balance for the amount of lifespan that university can take up.
The pack provides many more opportunities for teen sims to meet other teens too, whether at school or a boba tea shop or prom.
Rabbithole school is still available when desired.
The premades are cool.
My real-life human teen loves the build/buy. And the boba.
A lot of the other stuff that came with the pack - Social Bunny, Trendi, the pier (what's a beach-style pier doing in an old mining town anyway?!), the whole influencer thing, pillow fights confined to one bed object - got old really fast.
Edit: For your question about bugs, you should see the current list of HSY bugs here.
https://answers.ea.com/t5/Bug-Reports/READ-FIRST-Compiled-list-of-reported-Issues/m-p/11673025#M223852
The truly objectionable ones (like adult-child romance bars developing) have been fixed.
People randomly wandering into my house to demand to be best friends or go to prom is something I find a little annoying, and is not fixed yet.
If the high school graduation event were important to me, I'd be annoyed, because it often just doesn't happen, and even the designed timing is odd-- it's like the first or second Sunday after the student ages up to young adult, which could easily be after the sim is already married with kids.