I have cruised with ACL before, but the first time on a Modern River Boat. It's a little wider than the paddleboats, light and airy feeling throughout the ship. One very great touch that I enjoyed and the rest of the passengers, the Captain and his wife often ate in the dining room visiting with us at the table.
Our cabin was spacious and the bathrooms definitely bigger than the big ships.
If your looking to cruise where you can create lasting friends and memories the small ships of the American Cruise line is the way to go. They are more intimate but still areas of the ship where one can escape for quiet time to read or watch the Mississippi roll by.