The unique atmosphere and setting are what make this game worth it. Otherwise, it's another short platformer.
When looking purely at gameplay/story, there is nothing particularly interesting about this one. You pretty much are allowed to walk around, jump, grab stuff, and push the occasion button. None of these things are outstanding in themselves as they have been used over and over through gaming history.
However, when you look at the BW art style, the unique death sequences, the minimalist and ambient sounds, you recognize that the true enjoyment in this game simply is the quality of presentation. Yet, you don't enjoy it's presentation in the same way as you might an over-the-top exclusive with jaw-dropping graphics and cinematics. To the contrary, the stillness and simplicity stand in stark contrast to the majority of games out there so it does have a fresh appeal that draws you in and in many good ways.
In the end, is it worth the money? Well, it's extremely short and there is virtually no story to mention at all. However, if you want to be able to say that you've played one of the more unique and, indeed, fun little adventures this generation then you just might find the money spent a good investment.