I tried the newest version, where the gate on the first level takes you to the next stage. I couldn't get passed the 4th level, if you die in that level it respawns you in the 3rd one, and I felt a little frustrated after spending some time and effort getting past all the enemies in the previous stage. I liked the gadgets at your disposal, specially the smoke grenade, if you throw it while you are being pursued the enemies will stop looking for you, I liked that interaction. 

For the level design, It felt a little bare bones, specially with the cool mechanics you have with the different gadgets, the enemies patrolling, the rock-paper-scissors mechanic between gadgets and enemies... I would have loved to play around the environment instead of hugging the walls and waiting for the perfect moment to move, because the game has a lot of trial an error until you find the blind spot of the patrols. Adding some default walls or other places to hide around the environment will make the game feel much more organic and alive. Because adding more enemies into a room and call it a new level doesn't make a game better, and the level difficulty escalated really quickly.

I didn't quite like that the enemies detected you the single frame you enter their vision cone, you should make it more permissive to players. All stealth games give a couple of moment when the player is detected until the enemy realizes you are there and pursues you, maybe adding a sound cue when getting inside the cone and changing its color would be the perfect addition.

That being said, I truly believe you have a great game in your hands, it is an excellent prototype to try out all these mechanics. Also, thumps up to the artist, because I loved the art! If you continue working on the project, I can't wait to see the progress!