There is a common sentiment among artist that it's somewhat painful to view their past works. I don't understand or relate to this phenomenon. In fact, one of my favorite things to do is pick up old sketch books and see what and how I was drawing in the past.
My philosophy is as long as I try and do my best work everytime then there's no reason to feel ashamed or embarrassed in the future. Thinking this way really frees me up not only to look at my old work, but also keeps me from having self doubt about the projects I'm currently working on. I don't have to be the best I just need to do my best.