Well, the thing is that whether this artstyle is mediocre or not is just a matter of opinion. I happen to like it, for one.
Whether we like the style is a matter of subjective opinion ( personally I don't hate it, I just feel indifferent about it ). But I think it's fair to say that it does look like many other modern Indie releases, and could thus be considered mediocre, or at least rather uninspired. ( And I'd like to emphasize again that I'm only talking about the in-game style. The cartoon sequences and the general concept of the game seem quite original. )
Sure, as long as game development is not your only source of income. Obviously I don't know the particulars of these devs, but in the end it doesn't matter to me because, as I said, I'm totally OK with the actual looks of the game.
But still, judging the memorability and uniqueness of a game entirely by its graphics seems rather superficial to me. I'll take gameplay and story over graphics any day of the week.
The question is whether we want to view the medium of video games as mere commercial products, or works of art with a lasting value. This very website is full of games which weren't really commercially successful upon their release, but are now considered to be among the best and most original games ever made. Even if they were commercial failures for the devs/publishers at the time, they are now seen as valuable contributions to the history of video games, and major influences on current and future game releases. I think it's necessary to take risks to create something meaningful and of lasting value, especially for artists / creative types. It's either that, or the 25th sequel to Call of Duty and Assassin's Creed, which will be forgotten a few years after their release.
And the art direction and visual quality are certainly important aspects of a video game, but I was just generally speaking and this also applies to any other aspect of game design. Devs need to take risks regarding gameplay design, story-telling, music etc. too, if they want to create anything original and memorable. ( Whether this particular game succeeds in those sectors remains yet to be seen, but as I mentioned in an earlier post I do like the general concept, and will likely buy a copy. )