I'd always wanted to visit Rome since I was in my teens. OH and I finally made it 5 years ago. What a disappointment!
It was November but still overcrowded, scruffy, noisy and most things seriously over-priced. We felt like poor relations as we studied restaurant menus, bar prices, etc.
The good bits? Excellent city bus services to get around and you can buy a tourist bus pass in newsagents, corner shops etc. The metro is good, too. The general helpful friendliness of other passengers when they saw a confused tourist was a welcome surprise, too.
The off-putting? Most of what others have said plus the manic drivers. Even my OH, who takes most places in his stride, was rattled and said he'd be terrified to hire a car and set wheel on road there! Oh, and don't try to cross the road after the green man goes off. They will run you down!
The food - unless you go for a top notch 5* restaurant, most of the offerings are pretty dreadful. I had the nastiest lasagne I've ever eaten in Rome.
Quite honestly, I'd say if you have happy memories of Rome, cherish them and don't go back.