The churches in Rome are without a doubt, spectacular and breath-taking. Even the simplest and smallest churches there that I saw made the ones I've seen here in the US seem plain looking by comparison.
We visited the four papal basilicas, the Pantheon and stopped in at a few random churches we happened to be walking by. It's not hard to find a church in Rome. They're more numerous than Starbucks in the US. Seriously, you can't walk past more than a few buildings without encountering a church.
One of the first churches we wandered in to was Basilica dei SS Ambrogio e Carlo on Via del Corso.
Most of the other churches were similarly decorated. If you leave Rome without having stepped into a church or two, you've missed out on admiring a lot of artwork.