I read in a review, paraphrased, that this game would've been a wonder in a world where Portal didn't exist. I agree. This game is an alternative, and somewhat weaker, take on the first-person puzzle genre. Instead of working with portals, you have a gun that stores and fires various kinds of energy pellets which activate doors, walkways, or other machinery. Like Portal, the goal is to use your gun and the surrounding environment to progress to the next area. No actual portals to be seen, though,
The puzzle mechanic is actually quite decent, with the puzzles getting more complex with new elements being introduced at regular intervals. As in Portal, alternate solutions exist in some places. Moments of "Oh, duh! How'd I miss that?" abound. I found it a rewarding, and at times frustrating, experience.
There are also "bonus" rooms that require some out-of-the-box thinking, often utilizing a gameplay element that isn't used anywhere else in the game. As an example, and a slight spoiler (so, warning!) one bonus room can be solved by walking slowly through it rather than running, with the walk button being something most players forget even exists because it's not strictly required anywhere else. The bonus rooms were the most rewarding of all for me.
The story tying it all together is rather simple and weak, and gets thinner as the game progresses. The ending is a bit dumb. Where Portal was comedy-horror mix, this game tries to be more philosophical and sombre, delving into deep philosophy while still being accessible to regular folks, and attempting to do that in the interstitial moments between puzzles. It comes off more as pretentious and tryhard. The character you speak to, TOM, is an artificial intelligence, but unlike GlaDOS, he's working quite well, and he isn't much into jokes. This makes him a flatter character, but still, I have to congratulate the voice actor who did a wonderful job with what he was given.
Don't play this for the story. The puzzles are decent. The replay value is low. If you enjoyed Portal, this is a different flavour of the same product. I don't regret purchasing it.