Best time of my life

I did this program twice and it truly was the best two years of my life. I ended up placed in Lorraine on the border of France and Germany in a small city (both years) at a different high school each year. I know I got lucky, because my schools offered me a very nice two-bedroom apartment for free, and reduced price meals in the cafeteria. This was pretty common in my region, though.
In my city, there were three schools with TAPIF assistants and each school had an English and German assistant, so my roommates were German both years, which was really cool. (I shared the apartment with the German-speakers.) I wouldn't say the social life was incredible if you're thinking about going out and parties and things like that, but I was close with the assistants in my city and some nearby cities and it was an opportunity to meet some of the most like-minded, awesome people from all over the world. We still keep in touch and two of them I consider best friends - we still talk all the time. I lived at the crossroads of Europe and it seemed like people were always traveling, so there are always couchsurfers, students, etc. to meet, too. I got a chance to meet a lot of people when I was travelling as well, and I visited over a dozen countries. Every two months, we had a two week paid vacation. Even when we worked, it was only 12 hours a week, so there was plenty of free time.
My experience with the locals was not overwhelmingly positive. I had some minor issues with some staff at the schools (not English teachers) not being very nice (one woman was our neighbor and complained about us a lot, and another staff in the administrative office made fun of my French). Most of the English teachers were pretty friendly, some much more than others, but I never really got close with anyone. I actually never got close with anyone French at all, but I had a lot of friends. Frankly, my German roommates and the land right across the border stole my heart, and I ended up learning German and feeling more at home there. I struggled with the bureaucracy in France, too.
Some of my students (high school level) were awful, disrespectful in class, and one group even made fun of me. But I also had wonderful students who were AMAZING and so much fun. Both were kind of on extreme ends of the spectrum though; I felt that most French teenagers just seemed awkward and nervous. I worked with several English teachers and I usually saw each group of students once a week for an hour. Every teacher had their own rules. One teacher asked me to sit in her class and assist. Another teacher or two just sent me 2-3 students for oral exams each hour, and I graded them. Most other teachers let me plan my own lessons and do whatever I wanted. It was a tremendous amount of freedom, which I almost always enjoyed, but it could also be overwhelming for someone with no teaching background/experience or uncertainty about planning lessons. I wasn't given a book or anything. I loved that though, and I took lessons in a lot of different directions. We translated a pancake recipe French --> English and cooked American food with one group; we analyzed pictures in English and talked about discrimination issues with another... it was all so much fun.
I got a decent, if modest, amount of emotional practical support from the schools. The teacher responsible for me the first year... we never clicked at all, but she was there when I needed her. The teacher next year was much warmer. Generally, I can't say anything bad because they both helped me when I needed help, and staff would try to pass on other opportunities to me (field trips I could go on, opportunities to help two hours a week at a primary school after school program, things like that). I'd also add that the US TAPIF staff person in Washington was amazing, though I never had a whole lot of regular contact with her.
I got to experience TWO different cultures and see a French school from the inside. I got to meet amazing people from everywhere. I improved my French and learned German. I made wonderful friends. I loved the opportunities to travel, and all the programs I got to participate in... I au paired in the summers, did the WWOOF program, tutored the sweetest little boy. History and culture and all kinds of amazing things were everywhere around me. I felt safer there than I ever did in the US, although I walked everywhere. I loved the food, I loved the holidays in France... I absolutely loved the whole experience, I think about these two years all the time. I am happy now, but this was really the best time in my life (so far).
I also appreciated the level of freedom. I guess some international programs have more restrictions, but we were totally on our own (travelling, coming and going, etc.). I would also add that all of this is MY personal experience, of course. I'm sure a lot depends on where you are placed, because I met or heard of a few who were in small towns with limited transportation out, schools that provided them only a dorm room, things like that. I knew a couple assistants who weren't as happy as me, but I think in most cases it was more about their personalities (easily homesick, really "American," unsure in new situations, etc.). I think if you come into the program with the "right" attitude and an open mind, you'll be happy anywhere you go. Because really, you work 12 hours a week and the rest of the time you just get to be in France. :)