What do you like best?
Cheap and long term storage. However, getting your data back can be costly if you don't pay attention. They do provide an option by which to retrieve up to a certain amount of your data for free every month, but it's in the low single digits of percentage.
What do you dislike?
The retrieval fees can be astronomical if you're not careful.
I wouldn't recommend it for a long term backup solution, but as a long term archive solution due to these retrieval fees.
What's the difference? (This is my nomenclature.) A backup is something you want all of at one time (e.g. you restore a backup). An archive is something you might want pieces of from time to time (e.g. your tax returns for the last few years).
That said, I find Amazon Glacier to be exactly as advertised, and a very good price if you want long term storage with infrequent retrieval.
Recommendations to others considering the product
Pay attention to what your needs are. Again, the retrieval can be expensive if you're not prepared for it.
What business problems are you solving with the product? What benefits have you realized?
I no longer use Amazon Glacier. There are many cheaper and easier solutions that will hold the amount of data that I require (< 1TB).
However, it is so expensive to retrieve the data I have up there, that I currently am just maintaining the data I have present.