it got boring
It was quite repetitive.
Note: I only played till level 7, so I dont know if further levels included some of my suggestions.
Some Suggestions:
-You should make it so you only have to hold down the X or Z key to use it, instead of pressing it twice to turn on and off. Its easier and faster when you need to get out of a hairy situation.
-Have an ability to kill the enemy. I would have liked it if you could interact with the envioronment pulling switches and killing enemies. Or just with a knife behind them.
-More envioronmental interactivity. Like have a boss (green guy) in a locked room and you have to make it to another section to press the unlock button. The levels just need more variation.
-It would be better if you start off with no abillities then as you go, every 5 levels you learn a new ability, like invisibilty etc. And then you can go back to later levels and see if you can complete them faster
-Enemies need better AI. They should go up to the body and stop for a sec, then follow the blood footprints. Then look more around the area and search corners.
-It would be better if the AI wasnt so frantic. They are so random and too fast at turning. Great stealth games like MGS are great because the enemy have patterns, like all good enemies, to defeat them, you need to learn their patterns. Your enemies have none. If they hear you or see you, they should go check it out, otherwise they should stick to their path.
-Different areas would be nice, hire an artist and get him to draw some outside levels or sewer levels with big pools of acid that you can fall into.
Great job though, the sound effects and music are great and the concept is good, even though not a new one, I like the cool abilities too. The graphics arent too bad either.