When reviewing indie games, one has to keep in mind that there's a logistical constraint to them. It's small teams, sometimes even just a single person, and that can limit what one can do. On the other hand, one person can turn out amazing games. "Notch" did it with Minecraft. Phil Fish did it with Fez. Which makes it all the more aggravating when a one-man band turns out a game that fails to entertain. Hidden Deep falls squarely into that category.
Notionally inspired by horror classics as The Thing and Aliens, Hidden Deep puts players on a deep sea mining platform which has suddenly gone dark. A small team of engineers and security personnel are sent down to investigate what happened and get the platform back into operation. Players must move individual team members in side-scrolling fashion through various tunnels and shafts, activating equipment and dispatching the strange creatures which now appear to infest the facility to reach the end goal of each of the ten story missions.
Visually, Hidden Deep is painfully dull. There's a lot of browns and grays, with some industrial yellow for heavy equipment and reds for the enemies (along with the copious amounts of blood). And a whole lot of black. Lighting effects are not especially subtle for the most part. You're either going through fluorescent lighting in tunnels or bouncing around with your flashlight. There are few instances of natural or environmental lighting sources, and when they're used, they're not exactly awe-inspiring. The scale of the sprites makes fine details which could help the characters pop visually an impossibility. It's almost as if the developer couldn't quite decide on making a 16-bit side-scroller homage or a modern high resolution action adventure and tried to split the difference.
Sound is something of a mixed bag. On the one hand, you've got pretty good sound effects which fit with the setting. Elevators rumble, cranes and rail gondolas whine as they move, and creatures make distinctive noises including the wet splats of their demise when you put a bullet or two in them. But this decent, if workman-like, effort is offset by the tissue thin "soundtrack" and the uninspiring voice work. We don't even hear one of our hapless troops say anything (strained grunts and death screams don't count as dialogue) until the last mission.
While Hidden Deep lists Half-Life as an inspiration, the gameplay owes more to The Lost Vikings than anything else, with a hint of Metroid for good measure. Its insistence on moving team members individually means a lot of switching back and forth in missions where there's more than one character present, which can create problems. Players may be moving through an area that they haven't yet cleared and need to switch quickly over to the scout (who has the most firepower and bullets, usually), only to watch helplessly as a monster kills them. And if the character you're controlling dies, the mission restarts basically where they died even if another team member is alive. This scenario is exacerbated when you're moving through a notionally "cleared" area and enemies respawn for no reason. If this is intended to build tension, the practical upshot is only aggravation.
This is far from the only aggravation, however. Tooltips for how to use equipment are badly placed, and completely missing in certain instances where they would have been helpful. As a result, there's a lot of trial and error which sucks what little fun you might accidentally find. Character movement feels like it was based off QWOP instead of any sensible side-scroller, and is frustratingly unresponsive at times even with a keyboard. Hidden Deep boasts a physics engine, which is notionally to help facilitate the "realistic" swinging of ropes and the tumbling of blocks as your team members traverse the environments and interact with certain elements. In practice, though, it leads to a lot of unnecessary deaths when a character smashes into a wall and painfully slow traversals when using the rail gondolas. Compounding this aggravation is the needless "multiple lives" which seems to taunt you as your team literally kills themselves over and over again trying to get from point A to point B without being crushed, burnt, or eaten. This is doubtlessly tied to a challenge mechanic of some sort, but having it in the campaign is both pointless and annoying. I would say it breaks the willing suspension of disbelief, but you can't break what was never there in the first place.
If Hidden Deep is trying to convey a story, it is failing at every level. There's not enough environmental elements like graffiti or computer logs to provide clues about what happened. There are no NPCs who can be interrogated for more information like you would in Half-Life. Even your unseen boss talking to you on the radio can't provide any genuinely useful knowledge, whether that's how best to get to certain points or detailed background on the facility. There is nothing to draw players into the world, no narrative hooks, no opportunity for exploration that doesn't result in your gory demise, no characters to forge an emotional connection with. The levels are technically challenging, but they have all the narrative power of a lump of clay.
As a game, Hidden Deep is not a bad tech demo. But it is scandalous, even considering the Early Access label on Steam, that something like this came out in this state. It is the definition of "not ready for prime time," and any promised future content updates cannot possibly undo the awful first impression it makes.