I worked at Forever 21 as a seasonal hiring for Christmas.
Overall it wasn't a terribly bad experience. I made minimum wage and I got to say I worked retail for a while.
My biggest issue with the job was the lack of core management.
Over my time at forever 21 (which was 2 months), we had around 10 managers all working at the same time. This left most people confused. The biggest issue with this was that I would ask specifically not to be put down for a day, but another manager would put me down anyways without consulting the others, so lack of communication was definitely a problem.
My other biggest problem working there was the inability to move shifts around. My example of being given a shift I specifically asked not to have ended in being told I'd either have to give the shift to someone (no one wanted my shift) or get fired. So I had to cancel the plans I made weeks in advance in order to keep my job.