Originally released as a PC and Mac title, the first person abstract puzzle game Kairo is one of those games that you really never forget, developed by Locked Door Puzzle. Gameplay wise it's pretty standard, but in terms of the minimalist art and environments, strong use of basic geometric shapes and worlds themed after single colors, plus the feeling of isolation and wonder you feel as explore all make this game unforgettable. That's not to say that it isn't flawed, of course.
The game elicits the feeling of playing classics like Myst. You are the lone inhabitant of an ancient and dead world, full of strange machinery that is just as much magic as it is science. As you explore the world and solve puzzles, re-activating said machinery and breathing life back into the ancient stone systems, more and more you become curious about this world and wonder about the people that left it behind. That's not to say this is a story heavy game. There is virtually no text and no dialogue of any kind. All of this is told using the environment and playing the players imagination.
Puzzles are all pretty simple, mostly consisting of block pushing and stepping on pressure plates. That's not to say that there isn't more involved, but mechanically it's pretty straightforward. Maybe you're walking through a maze but the walls don't appear until you approach them, or you have to press buttons in a specific order to activate a beam, or recreate a certain symbol. Puzzles can usually be solved in any order you choose, and while they can be frustratingly difficult sometimes, there is a pretty solid hint system for the apathetic or weak willed.
One big issue I have with this game are the controls. Without a keyboard and mouse, it feels pretty stiff overall. You look around by swiping, and move forwards and backwards with two arrow buttons. But there is no strafing, and no ability to jump. Basically, these are first person tank controls, and while they are manageable, they make certain tasks much more difficult than they need to be. All of that aside, this is an incredible game, in a genre and style that you almost never see at all anymore, let alone on mobile. I thoroughly recommend finding the Mac and PC version if you want the best experience this game has to offer, but this mobile version, for just under five dollars, more than suffices.