These are not first impressions, but things I experienced over 6 Sim weeks of play with a household of 6 teens. I sent 2 of them to school each day (a different 2).
Personally, I think the high school is designed well. My Sims had just enough time to take a shower downstairs in the morning if they needed. The boys', girls', and unisex bathrooms are color-coded -- red for boys, green for girls, and gray for unisex. They mostly socialized between classes, but there was time at lunch to paint a picture or play a game of chess. A possible bug is that your Sims can't go to class if the whiteboard has been pranked; they have to wait until it's been cleaned off. Another possible bug is that your Sims with the goal-oriented aspiration will want to clean the whiteboard, and I'm not sure that's possible.
Prom was great. Kudos all round to the developers. Your Sims don't actually have to ask anyone or be asked to go; at 7 pm, you get a pop-up asking who to send to prom. Only teens are eligible. If you want a Sim to be either royalty or jester, have the Sim's date vote.
The after-school activities are generally a disappointment. Occasionally you get a pop-up, but Scouts and Drama Club are more satisfying in that regard. Scouts and Drama Club do not count toward the goal-oriented aspiration. Your Sims will get banners when they reach level 2, and a trophy at level 3. They also get a trait -- Chess Master, Cheer Champ, etc. I sent Sims to the Football and cheerleading activities only once.
Graduation was so-so. It does exist, if you don't take early graduation for your Sims. My Sim was valedictorian, which might be why he didn't show up in cap-and-gown. He was the last to get a diploma from the principal. 3 students in cap-and-gown did get diplomas. They take forever to go up to the stage, though, and start wandering around the room as soon as the valediction finishes. Even though my Sim was in street clothes, he threw a cap up in the air at the end.
Social Bunny was fun at first, but tiresome after a while. My Sim who was going for Admired Icon, never did complete the aspiration. She was supposed to have 250 followers on Social Bunny. She had over 2000, at least 250 whom she gained after reaching level 3, but the aspiration never completed. If you don't want your Sims to get mean texts from their parents, don't add their parents as friends.
Crushes are great if you like surprises.
The Pier is fun, but I don't know whether it's good for dates. The problem is that you have to send your Sims somewhere else for the date -- to the park usually. So they go on a ride, you queue up a second ride, but they have to walk back to the park after the first ride before they talk to each other again. The pop-ups for the haunted house and tunnel of love are cute; I don't know if there's one for the ferris wheel.
Finally, if you put your Sims on the Gallery after they go to high school, it will be as if high school never existed. They'll have the character traits and lifestyles they earned, but the traits like Cheer Champ and Valedictorian won't be there.
All in all, I got my money's worth, but there are disappointments and annoyances.