IES Paris is challenging, but worth it.

Honestly, I was so anxious about studying abroad before I left the US. It seemed like such a huge undertaking, and I didn't exactly know what to expect. However, IES did a fantastic job of helping us students acclimate to our new homes. The staff is really friendly, and they are more than willing to answer any questions you have. They organized a lot of outings that help you get exposure to Parisian culture, and one thing that I really appreciated is that they never made me feel like a tourist. They really want you to feel like a resident, which I think made the whole experience so much more meaningful.
If you want to get the most out of the program, I would HIGHLY recommend setting up a homestay arrangement. I loved my host family; they were so welcoming and gracious, not to mention adorable and awesome. They offered me a lot of classic and unconventional French foods, provided suggestions on things to do in the city, and helped me develop my language skills in a new way. They were amazing, and I class myself as lucky that I got to spend four months with them.
The last thing you want to do while studying abroad is actually study! But with IES you are required to take five classes each term, no matter how much you want to deny it. The classes aren't too terribly difficult. My experience is that you get out of it what you put into it; if you don't want to learn about the subjects, you probably won't learn anything, but if you actually do care about your grades (which I did, because I'm a goody-goody), you can get a lot out of them. Classes are all in French, which adds a whole new level of difficulty to the program.
If you're interested in taking a class at a real French university (such as the Sorbonne or the Institute Catholique de Paris), I'm going to warn you right now: my ICP class was the HARDEST class I've ever taken in my life, but after I was finished with it, there was a huge feeling of accomplishment. I would advise that you only take an exterior class if you're up for the challenge.
Ultimately, I appreciate the experience of studying abroad more than I can put into words. It's not just a matter of developing your language or visiting museums; it's about testing yourself, pushing yourself to master new challenges, and learning more about yourself both as an American and as a world traveler. If you're willing to give up some of your old habits in favor of new, exciting exploits, then by all means, go for it.