Dark is an interesting case for a reviewer. It's so successful in delivering on it's description ("a very dark, atmospheric puzzle-platformer"), that it becomes somewhat pointless to highlight, or be distracted by, little technical flaws. The reason why I believe players will enjoy Dark is because is offers a less-common, shadowy and atmospheric platforming experience for $1 (80MP). It's another great example of a wise and low investment for anyone looking to kill 30 minutes doing something very different from the mainstream gamer. So let's get digging.
My point is... you won't be playing Dark for the typical skill-based platforming action. In fact, you can't die - and there are no enemies. There are puzzle elements, but with no sense of urgency - and there is a "collect the sparkles" element, but with no real implications. Dark is a game that just wants you to play it so that you can be a part of it, not so that you can overcome it, master it, dominate it, or hone your skills on it. The first time I saw another moving creature, I wrongly assumed that it could hurt me. I had to laugh at how pre-programmed we are in the platformer genre - I was jumping on the other creature wondering if he need 3 hits to be killed or something. Nope. :)
So obviously, that "non-skill" or "non-action" approach doesn't really work if the game is cut from the same artistic mold as other platformers. But Dark will draw you in with atmosphere. Simplistic shapes, lots of lighting/shadows, a rather heavy dose of physics, and mellow ambient music create the sense that you're really just here to soak things in and take part in the experience. The only true goal is to progress and maybe to explore if you so choose. At the end of a hectic day (and a whole week without internet - oh the horror!) I actually found this simplistic approach to be calming and relaxing.
Dark is not a long game - clocking in around 30-40 minutes max. Again, it's like jumping in to another world for a quick relaxing adventure - which, now that I write it, realize that's pretty much what video games are all about. I actually thought that Dark got better as it went along - the first couple levels are pretty standard, and I actually hit a couple technical snags (got stuck in some physics, blocked from moving) in the earlier levels. But the last couple levels are more interesting, colorful and dynamic. All of the way through the last 10 minutes is a good time, including the credits.
A couple small gripes - first, the jumping was not as clean/natural as it should be. You can't jump from certain surfaces, which was frustrating at times. As first mentioned though, you're not really in any danger so the lack of polish on the movement/controls doesn't have the downside of frustrating and unfair deaths. Second, for a stylistic venture, I feel like the main character could have been better designed to have more personality. While the heavy lighting and shadow effects help mask that somewhat, the basic diamond shape with googly-eyes just didn't do much for me. A main character with a bit more depth (and maybe a handful of simple expressions) could have taken the immersion and character/player-connection up a notch.
Overall, I recommend this as a good value, not so much as a platformer - but just as an experience. A video can be seen on the dev's website here.