On our trip last Nov/Dec, we went to HS once from 11am until close, and once for early morning magic until about 11am, so we spent about a full day there, over all, plus early morning magic. I expected Hollywood Studios to be our least favorite park. I had been reading so much about Animal Kingdom being a half day park, and wondering why there didn't seem to be nearly as many people saying the same of Hollywood Studios, because I just didn't see that there was so much to do. I was so happy to be wrong.
We did not do Rock n Roller coaster (both kids too short to ride), but we did to Tower of Terror. Here is a rough itinerary of what we did:
Indiana Jones Epic Stunt Spectacular
Tower of Terror (FP)
Beauty and the Beast Live on Stage (fastpassed this, but probably didn't have to)
Long lunch @ Hollywood and Vine
Star Tours (FP)
Disney Junior show (during seating, I scored FP+ for Toy Story, which we had not planned on riding this day)
Toy Story Midway Mania (4th FP)
Frozen singalong (5th FP, unnecessary)
Voyage of the Little Mermaid (6th FP, definitely unnecessary)
Great Movie Ride (I think standby, as this was the only line we waited in more than 5-10 minutes all day)
Rider swaps for Tower of Terror and Star Tours
Fantasmic!
The best part is that we didn't do nearly as much walking and standing in line as in the other parks, so we still had life in us at the end of the long day, which had started at Animal Kingdom EMH.
The second day, we did Early Morning magic, where we signed up for Jedi Training Academy, met Mickey, Minnie, Olaf, Buzz, and Woody, and rode Star Tours and Toy Story again. After breakfast,we did the Jedi Training show. Then we hit Toy Story one more time with a FP that a cast member gave to my 3 year old when they traded pins (he also scored a toy monorail and extra pins that day because he was just so happy and friendly to all of the cast members, but that probably has no bearing on YOUR enjoyment of HS). On the way out, we met Donald Duck in his sailor suit, which made my day because I didn't realize he was available for meets anywhere.
If you don't have little ones, skip the Disney Junior show, as that's the only attraction my husband and I did not care for (the kids liked it though), possibly because we had to sit on the floor, while trying very hard to be comfortable and not invade other people's personal space. And, obviously, Great Movie Ride is no more, so you can't do that one. However, honestly, we spent almost no time in lines at Hollywood Studios, and got lucky with extra Toy Story fastpasses. I don't think we would have been able to do all of that in a single day.
So if you think you'll like the shows, I think there's a full day for you there. It was actually really difficult for me to plan times to see all of the shows and make sure there was time to get to the next show or attraction.
Oh, and we also dropped in for Fireworks at HS on our first night, and saw the Muppet show before Jingle Bell Jingle BAM.