Never get bored of the view of the Pantheon as you turn down a little side street and it opens up in front of you. Rome was my favourite city years ago but then l went to Florence and NY after, those are definitely my top 3.
I've been twice (would love to go again if the planets could align!). First time in 2012, then I think it was either 2017 or 2018. Both in early March. The Spanish Steps, first time was busy, the second time was insane. You couldn't even get up the steps for youths sat on them. The Pantheon was relatively quiet inside, but outside, it was heaving. And if we wandered by, there were always tour groups and tut sellers congregated in the square. Similar with London though, head one street over from a key tourist sight and you'll often have it to yourself.
First time I went was 1979 (have that for being an old git) and a few times after that. The last time was just before Covid struck. (2018?) The big difference is the traffic. In 79 it was absolute mayhem – no lanes, no speed restrictions, everyone using their horns and / or shouting at each other all the time. Traffic light meant nothing, The noise across the city was incredible. I’ve never done a parachute jump but the fear and uncertainty couldn’t be much different to crossing the road in Rome back then. The trick was - simply walk out and cross at a constant pace. Not easy when everything seems to be aiming directly at you before swerving at the last second. Walked across that wide road around the Colosseum once. Think I had a little cry when I got to the other side.
More to see and do in Rome than any city I've been to and Ive been to a lot. There's ancient buildings around every corner. All of the tourist spots are worth visiting. The Pantheon and square at night were brilliant but that may have been because we were treated to a Claptonesque guitarist for most of the evening. Get tickets for the Vatican museum otherwise you might be queuing for hours. The wealth in that building would pay off the third world debt. You need at least a day for St Peters Square, Vatican and museum. Spanish Steps and Trevi Fountain are quick stop offs as you're walking around. Coliseum and Roman Forum are another half day and if you like the inside of churches there are dozens around the city. Travastere is the place for eating but also the square around the Pantheon was good I'm sure you'll have a great time.
Loved Rome but like you did a flying visit. Colosseum. (Would have loved to visit inside) Pantheon . ( as an aside they were Filming Angel's and demons when Tom Hanks walked across the sq. And handed a bride over to her father. Getting married in the building) Trevi fountain Spanish steps. But would love to spend a few days there to see more sights. Eg. Vatican. Basilica etc. https://activebeat.com/travel/12-things-you-cant-miss-in-rome/
Borghese Gallery Do not miss it Book in advance Otherwise, the rest of Rome is just about the best place to visit in the world.