I can understand why some people may get filtered by the first 2 level packs - they are very straightforward - basically with a single possible path to the goal. But I understand it - the first pack lets you get the hang of it, get the feel for it, second one teaches you to think with portals. 3rd pack is where you need to start thinking, aaaand I got filtered on level5. Well, not filtered - I genuinely feel like it's impossible since I couldn't backtrack a route from the goal too far.
But I think it's a great start for a great puzzle game. I think you have something very solid cooking here. It may be not for everyone since spatial thinking is hard, and I can imagine how hard it is making levels. But it's a good start. A very solid start.
But please, provide a binary next time. Playing in browser is very annoying.