While it will feel like you have stepped aboard Rapture (Bioshock), you haven't. Though the atmosphere certainly feels the same, the game never gives you a weapon. Like Rapture, though, Helios is an amazingly well done period piece, and it is beautifully rendered. It is also creepy as ever.
As far as game play, it's a linear problem solving game that tells a story along the way. You don't really notice how linear, though, which a testament to the creators. Still, only a few areas allow for exploration beyond what is required for the story. For the most part, you are piecing together what happened while trying to accomplish certain goals.
I definitely enjoyed playing it, though it was fairly short. I believe I played for about 8 hours total, finding most of the collectibles. Definitely worth the play through, though. The whole experience was worth it.
The only real complaints I have are pacing issues with certain challenges, and some challenges that require a bit too much in the way of perfect play. Outside of these few scenes, the game really only requires you to look around and pay attention. I get the desire to build up the tension, but the are points where, if you are being chased, and you make a single mistake, that's it. You might as well just kick back and enjoy the cut scene one more time.
In fairness, the scenes are incredibly tense and scary, and they definitely get the old heart pumping, but it feels a bit unfair to make the timing THAT tight.
The other complaint is that the game telegraphs a certain twist very early in the game, but there is nothing you can do about it. Rose isn't nearly as observant as the player, apparently. Again, totally understandable - this is really as much an interactive novel as a game - but mildly annoying when you figure something out hours before the protagonist does with no way to avoid it.