In my honest opinion, Alter echo is not a game of legendary proportions, but it is a great game that should be more popular than it already is.
What this game is about, is you are a Shaper named Nevin. Shapers (in a science-fiction universe) basically bend a substance called plast, which was created by the first Shaper and the best one, Paavo. This substance was later used to create all of mankind's structures, tools and even starships.
You crash-land on a planet far away from earth to retrieve Paavo for whatever reason, and must get to Paavo.
The game features a mechanic that changes your body's form between three different ones. The Sword (your normal form), Your Gun (A big protoss-looking thing with a gun), and Your Stealth Form (Lizard thing that cloaks). Each enemy in the game can only be killed with one form, and many areas require changing inbetween these forms to kill enemies and to accomplish unique puzzles.
Time Dilation is a puzzle that is completely unique to this game. This puzzle type is mandatory in many places, and is based on a time constraint. If you do it right, you can proceed into new areas, but you can use it to deal great damage nearby at any time, the tougher or more enemies, the harder the puzzle is, and the faster you must be.
The soundtrack is amazing, nothing short of it, the environments are rich and varied, even stunning for it's generation, and there are no huge difficulty spikes, save for at the final boss.
This game is easily my 4th favorite game among Galactic Civilizations 3, Starcraft 2, Mass Effect 3 and in my honest opinion, it deserves the sequel it is wide open for a hundred times over.
Easily more challenging than any game I've played nowadays, with Dark Souls 1 and 2 and even Demon Souls under my belt, the challenges are all balanced excellently and it has great pay offs with a fantastic story.
It only gets an 8, because it's not gotten any real ports to current-gen platforms.
It just... It is easily the most fun and best game I've ever played.