Did you ever think to yourself "Man, Portal is too easy. I wish Valve's playtesters hadn't weeded out the 5 emancipation grid room, or thrown up when walking on the ceiling"? Well, you're in luck.
This game is, from my vague knowledge of Metroid, a hybrid of Portal and Metroid. You are a scientist, stuck in his lab, with all the areas therin sealed off by devious puzzles only solvable by your gateway (Portal) devices. Yes, devices. You get the basic one early on, but then you find yourself needing to rotate gravity, and link time AND space, and make yourself small (or large, but I managed to Portal all the large situations) through the same device. As you get more unlocks, you can explore more of the map, and open up harder puzzles.
This doesn't have GLaDOS, but the cruel puzzles make up for it (you can buy automated solutions for just 25 hint orbs, but generally the 5 orb "Is this possible yet?" question is more entertaining).
If you want a very much easier platformer with the same time mechanics as here you can check out Shuggy by the same dev. But it is very very easy, and I'd only recommend it to kids. Seasoned platformers are going to find that the only challenge here is trying to complete two player co-op with one character on each hand.