TXCityAggie said:
I think Rome needs 3 full days minimum. Vatican City and the ancient Roman sights each take a full day each. Then you need a full day to just walk around and enjoy the city center.
To elaborate on this - we were there for 2 full and one partial days early last June. I think the Vatican alone requires two mornings - and here is why: both the museums and the basilica are must-sees, and I really enjoyed climbing to the top of the dome (it's an absolutely stunning view). That needs to be done early in the morning, otherwise it is just too crowded and miserable (it's an extremely small space). The Sistine Chapel is also best seen first thing in the morning, before it gets too crowded. So, this pretty much means two trips to the Vatican.
The day we climbed to the top of the dome, we also did a VIP tour of the Colosseum (with the Walks of Italy company I mentioned above). That was in the afternoon, and while the main part of the Colosseum was crowded, with this particular tour company, we had access to parts where no one else is allowed (we actually toured all three levels), so there were parts of the structure that our group of maybe 20-30 people had completely to ourselves. I can't say enough good things about that tour.
The same idea applies to other landmarks like the Pantheon and Trevi Fountain. If you want to really see the beauty and details up close and not be mobbed by crowds, it's best to visit first thing in the morning.
With 2 1/2 days, what I mentioned above is pretty much all we did. And we really didn't get a good tour of the St. Peter's because I saved it for the end of our Vatican Museum tour, and by the time we got there it was ridiculously crowded to the point that it was not enjoyable (we should have gone in after we climbed the dome the day before).
We didn't have time to visit any catacombs, visit Castel Sant'Angelo, or visit any of the Vatican gardens, all of which are things I would have enjoyed.
I know part of our experience was due to the fact that we visited in June, but all of our tour guides told us that the city has been more crowded since Pope Francis was instated. I suspect April would be more pleasant, but some of these attractions (like the top of the dome) require very few people to become unpleasantly crowded.