Got this game during the weekly sale for $0.99 USD, and it is definitely worth paying and playing if you enjoy action platformers.
If you like platformers, chaining different combos for that wonderful score multiplier, and large areas to explore, then you will really like this game.
The aesthetics are very good with lots of detail in the environment. The music is nice and is appropriate for the action and atmosphere.
The controls are not overly complicated, however, chaining different combos can be fairly challenging. The learning curve is moderate, again with most of the difficulty due to the combos (if you care about increasing your multiplier to maximize your score). I strongly suggest using a control instead of the keyboard. You do not use the mouse when you play this game (even in the menu screen).
I think the game may not be fully optimized for Windows 8.1, as I cannot seem to be able to change the resolution to anything besides the default (1280x760 i believe). If I change it to anything else, the game appears to zoom into the top left, so it seriously obscures your field of vision (impractical to play this way). I do not believe there is a resolution fix at the moment.
The game starts off with a helpful tutorial that lets you most of the available skills - its similar to the original Assassin's Creed where your character is maxed out, then you start the real game debuffed back to level 1. You even get to see the stats screen that strips away all of your skills and levels.
You have 4 different suits: regular, fire, ice, and earth. You can switch to any at will, but the elemental ones drain energy - and you will automatically switch back to regular Zack once you deplete your bar (it refills fairly quickly). Each suit has different abilities and uses. For example, the fire suit can shoot fireballs (surprise!), glide in the air, and also moves the fastest. The ice suit can slow down time (extremely useful for navigating through numerous environmental hazards) and use ice attacks, freezing enemies. The earth suit cannot jump, however, it is essential for breaking through destructible obstacles and getting to secret areas.
During combat, if you switch suits and vary your attacks, you will boost your multiplier (resulting in boosts to your score). This can be tricky to master in the beginning, especially if you are not using a controller as the keys bindings are very close to each other. The game progresses in difficulty at a reasonable pace. The first few boss fights were pretty easy to defeat.
As you pick up the collectibles, you will gain experience for levelling up. I am pretty sure leveling up is automatic, as I have not been able to select which skills to invest in (mind you, I did not get very far into the game at the time of this review). There are secret areas with collectible trinkets for the achievement hunters. The stages are pretty big, allowing you a lot of space to explore.
Overall, I think any platformer junkie should give this a try, especially if you love chaining your combos and watching that multiplier go up. There is a scrolling bar that provides feedback on your score's global ranking, as well as its comparison against any of your friends who may have the game.