I'd like to start this review by saying that I have some mixed feelings about this game... I really like the concept, but I might have done a few things differently on the execution.
Firstly, I'd like to give a little overview of the kind of game this is:
Eidolon plays fairly simply as games go. It takes place sometime in the future (it is not clear exactly how far). You wake up somewhere deep in the forest in Washington and you need to explore to find out where you are and what happened to the place you are exploring. This is done by walking. Lots of walking. Lots and LOTS of VERY repetitive walking. Thankfully the developer did include a way to push a key for auto-walk so my "W" finger didn't get too tired. Still though... you walk incredibly slow and the map basically covers all of the greater Seattle area including the Olympic Penninsula... and while it may not be "to scale" it certainly feels like it due to the time it takes to get from place to place. It would seem like the gameplay is meant to feel immersive and realistic, although the graphics are very artistic and simple due for the most part I'd imagine to this being an indie game that is meant to be able to run on a lot of computer systems (did I mention the HUGE map size?) I'm sure there were other creative reasons for the particular graphical style chosen, but I won't get into that really... it suits the game fine and it doesn't need to be "realistic" to get the appropriate feeling across to the player.
Okay, back to the gameplay... near your starting position you can find a few items to help you in your journey: a compass, binoculars, bow & arrows, and a fishing rod. All these items are useful in either staying alive, or finding "clues". The items and clues both appear in the form of flashing orbs that float above the ground: white for items, green for clues. Clues can be either a map of a portion of the game area (usually in a hand-drawn style) or snippets of paper letters, notes, or sometimes photos of events or people that have been in the area before you but are now gone. I don't want to give away any of the contents of the clues in the explanation of the game-play, so I won't say more about them. Instead lets focus on the process of obtaining said clues. These glowing orbs you will find clustered all over the map... there are a LOT of them. Each one has a link at the bottom that, when activated, sends some flashy lights flying off into the sky in the direction of more clues that touch on that subject. Unfortunately, you will spend the majority of the time playing this game in-between clues just walking from place to place. It starts to feel very tedious after a few hours... Did I mention the HUGE map size?
Okay, sorry, getting distracted again... So clearly finding these clues is the driving motivation behind playing this game. I actually really enjoyed the part about discovering the history of the area and what happened to make it so different. There are some very well thought out stories explaining the events that took place that "ruined civilization" (I don't think that's giving away too much... I'm still trying to keep this "spoiler-free") So now I'm finally going to go into the part of the game I wasn't so satisfied with: In order to travel from place to place you obviously have to traverse the natural envirionment. You can sprint, which I highly recommend because walking is PAINFULLY slow, but only until you get tired and have to sleep, and sleeping makes you hungry when you wake up. So, aside from a lot of walking, which I think I've mentioned a few times now, you will also have to gather food and eat it to keep yourself from starving, one of two ways that I think you can die in this game.
(Quick disclaimer: I haven't tried dying to see what happens yet... not sure if you lose all progress or what.)
There is plenty of food to find in the game, though the bow & arrow was next to useless as you can't aim with it well enough to hit a moving target. Despite that, I didn't have trouble finding enough food to keep me from starving. The other way you can die is by freezing, which is fairly easy to avoid so long as you stay out of the water and don't climb any mountains. You can swim in water for a short period, but if you stay in too long I assume you die of hypothermia.
In the wilderness you also have to avoid predators... they will attack if you come too close or try to shoot them, which brings me to my biggest gripe of this game: wounds. Unlike most "survival" games where you have a health bar of some kind, Eidolon instead has a kind of system where whenever something bad happens (eg. you fall from a height or get mauled by a predator) you pass out for a few hours and wake up with a "serious wound" which either heals over time... or doesn't. This happened to me several times while playing and kinda caused me to stop eventually. I think there is nothing wrong with the system of getting hurt... that keeps with the realism of the game and the seriousness of surviving in the environment. My issue really stems from the system for getting BETTER. When a wound gets better on its own you don't have anything to worry about... however when it becomes infected, it won't go away. In addition, it causes you to become "ill" which wastes a lot of your food becuase you can never stop being hungry, and makes you have to sleep a LOT (which uses up even more food). Most of the time you have a "festering wound," you will be ill. When this finally happened to me from falling off a ledge in the game, I nearly quit on the spot... however I wanted to see if there was a way to heal the wound, as it says something about "put an antibacterial on it" in the game interface. After hunting around the steam forums I found a post that was somewhat helpful... it said there was an item called "honey" in the game that you supposedly find in beehives up in the trees that will work. Only one person had ever found it by the looks of it, but if it does exist in the game, I never could find out where. There was only one other thing in the game that can cure wounds, and that is a special swamp. I happened to have found said swamp earlier in my exploration because it is not too far from where you start the game, but it contains some warm "brown" water with floating will-o-the-wisp lights over it that miraculously cures all wounds and illness instantly... this would be great except that when my wound became infected, I was probably about a 5 hour walk away to the north (this swamp was in the south-east end of the map). And did I mention that you have to eat a LOT more when you're ill? That means stopping to fish or collect berries almost constantly, and then you have to keep sleeping so you can continue running instead of walking, because lets just say a 5 hour run is a lot longer when you're limited to walking. So needless to say I just wasn't up to the time commitment. I had to finally resort to console commands to try and free myself of the festering wound.
I am probably almost out of space here, but I didn't really get to mention the day/night cycle with weather... It goes from foggy in the morning to clear in the afternoon, to dark at night... with rain mixed in a lot. Which is accurate to the region, but it makes the exploration really annoying when you can't see where you're going half the time.
Also, there were a few bugs... mostly things that break immersion like floating grass and stuff, and campfires cast no light on the surrounding terrain. Nothing major.
The only part about this game that really feels broken to me is the inability to cure wounds that become infected. If you're going to say "put something antibacterial on it" and then give a decent percentage of the inflicted wounds infections... PUT MORE ANTIBACTERIAL ITEMS IN THE GAME! Seriously! If beehives do exist, they should be a LOT more common. It is a critical design flaw, in my opinion.