I used to subscribe to Birchbox but after about a year I realised that I had ended up with a basket full of samples (and even some full-sized stuff; they do send those, too) that were all completely unused. I loved getting a box in the mail each month, but I felt like I used so few of the products I got. I'm the kind of person who has fifteen lipsticks that are all virtually the same shade, though, so maybe I should have expected that luck-of-the-draw colours weren't going to work for me (also, sensitive skin, which kind of turns me off using any new skincare just for the heck of it).
If you're adventurous with beauty products, though, you might love it. It really was a lovely little surprise to get my box each month, but for me in the end I felt like it ended up being a waste of money.