I normally judge tabletop games based on a few select criteria; mechanics, which splits down into ease of use, effectiveness, and how well the mechanics fit the underlying theme, and setting which is a sum of overall game feel, the attractiveness of the world the game takes place in, and how much there is to "do" in the setting, i.e. how many different types of adventures the core material supports.
In terms of ease of use, Shadowside has the potential to confuse newer readers; Jacob's Ladder is a far stretch from what is done in other popular RPGs and the World Turtle takes a second to get used to. However, once you have taken a second to read through the explanations of these mechanics you'll find that they are very intuitive. Outside of using the latter, the game is a simple system. Finding out what you have going for or against you is simple addition, while the Storyhost (the game's term for Game Master, Storyteller, etc.) handles the difficulty arrayed against you. From there, you simply check Jacob's Ladder and roll the dice. While this system may seem intimidating early on, it cuts down on a lot of math and keeps the game flowing, only briefly stopping for the single roll and to check the Ladder.
Effectiveness is also covered above... the system not only uses mechanics that effectively pull together all of your advantages and disadvantages into a single roll, it also encourages a degree of success or failure system, trusting the StoryHost to make the best use of it instead of providing rigid guidelines. In terms of the character sheets, while the World Turtle may seem complex most of its traits are derived, making character creation easy. Besides the Turtle, the sheets are bare and simple; your skills, a bit of backstory, that's it. The sheet might benefit from a line for items, however.
Unlike a lot of games, the mechanics really do a great job of reflecting game feel, and the setting and game feel influence the mechanics. The game COULD have had a simple list of surface traits and core traits in plain text, but instead it uses the world turtle. It could have had a simple grid in which you compare your Might vs Difficulty, but instead it uses Jacob's Ladder. The resource system even ties into the lore of the setting; a belief system, that represents the amount of faith you put into your chances of success (and thus how it is reflected in the Shadowside), how these beliefs can be drawn on and how they can be damaged when things go south. The mechanics really make the game feel more alive, like the setting permeates everything about the system. It is spectacular.
As for the setting, the game feel is spectacular. It is an immersive atmosphere of conspiracy theory, the paranormal, and just outright creepiness that fits all the more because of how similar the setting is to our world. In fact, for someone without knowledge of the things going on behind the scenes, it is our world... which makes it feel all the more real, all the more spooky. It hearkens back to the old days of World of Darkness, and interestingly enough could also benefit from a warning that The Shadowside is just a game, despite how close it gets to reality.
The setting itself will draw in a similar crowd as WoD (it has Vampires, Mages, Werewolves, Voodoo, Mad Scientists), but also strives out on its own into uncharted territories. The Shadowside is a supernormal place were belief actually becomes truth... leading to all sorts of interesting implications on religion and reality in the setting, especially when people start using its power in the real world. The factions are all a nice mix of oldschool paranormal above, but also some great potential for more, as evidenced by the SCaV3NG3R "faction"; a disorganized, ramshackle gang of people who ended up a part of the picture through following ghost stories or conspiracy theories, whose only ties are barely coherent online communities, and whose powers are like a combination of Ghost Tricks, /x/ sigils and stage magic. Anyone who has ever been interested in conspiracy theories, ghost stories, or the occult should get great enjoyment out of The Shadowside.
Finally, despite the brevity of the rulebook, the setting allows for hundreds of different types of adventures with a little imagination. Players can play Catholic Knights who are bringing about the next miracle to fuel their god with belief, or play SCaV3NG3Rs taking their first delves into the Shadowside. A group of new inductees to the Greater Thelema Society sabotaging each other in the Shadowside in an attempt to find their companions first. A ragtag group of runaways meeting up with the Sisterhood of Salem. You could be agents of the Accelletrix working against their detractors, or you could be a brutal Somosa shaman butchering the innocent to provide for their people. The possibilities are nearly endless, with the system equaling supporting combat, social gameplay and investigation.
All in all, Shadowside looks like it could be the next bug cult hit, and I look forward to any new material concerning it.
[5 de 5 Estrellas!]