The lush lawns and amazing artwork in the Vatican is absolutely breathtaking. I'm Jewish and I still felt a sense of awe while visiting this tiny "country."
Give yourself a lot of time when traveling to the Vatican, because the line to get in is about an hour-long wait, even during the off season. Also, girls must have covered shoulders and cleavage. It was very humid the day we went (of course, it was the middle of June). So I suggest you layer with a light shirt you can take off after you leave the Vatican walls. We first went into the Sistine Chapel. I thought of all the slides I saw in my art history class. They don't do the works any justice. All the pictures you have ever seen are nothing compared to the real thing (unlike the Mona Lisa, which I wasn't too impressed with, but that's another story for another journal).
I didn't feel any religious weight while in the Vatican, but I did feel the weight of history. I thought of all the men who had walked through the courtyard before me and all the decisions that they were making.
There is daily Mass (multiple times a day) held at Saint Peter's Basillica. There is a section off to the side for pews, while the rest of the church is open to tourists. If you are of the Catholic faith, you are free to sit in the pews (prayers in Latin, of course).