Hello there! Hopefully I can help. you with your questions!
1. Most people do not have any bad experiences with this program however it is not impossible. Some people get stuck in a role they really didn't want or a ride/location they did not want which can damper their program but you can make the program as good as possible by surrounding yourself with friends. Some people also don't get the best leaders which can hurt your program but its good to keep in mind a leader or coords are just there to make sure you are doing your job so if you are doing it correctly there is no issue.
2. Some downsides are definitely if you are a home body, you may become homesick in the beginning because I know it was very weird to see families being together and happy and I was just alone but once I found my friends it didn't matter anymore. Also like I said above, getting the role/location you really didn't want could damper your program however I know people who hated their location in the beginning and loved it in the end!
3. I just finished my program (August 12th-April 30th) since it was cut short in March because of Coronavirus. I found out I got Toy Story Land and was so excited and thought I was going to get Slinky or Mania but I got Aliens and I was a bit bummed in the beginning. However, I made it the best I could because I had the best friends I could ever ask for at my location and we had a ton of CPs there. I also had the best coords in the entire world so this definitely made my experience so good that I actually extended my fall cp through spring and I don't regret a thing. These people have changed my life and helped me come out of my shell and I couldn't have asked for a better group of people (cp, pt, ft, ct) to work with! I miss them all so much <3