Quick impressions for Pixel This!:
Well, I'm a huge Picross fan, so reading the post by the creator I immediately downloaded it. I have to say I'm a bit disappointed because it feels like this is a pretty basic/beginner picross app. You have 40 5x5 puzzles as 'starters' then you move on to 20 10x10 puzzles with an animal theme. There are, I believe, 4 more 20 10x10 puzzle packs, each with their own theme, but those are IAP. I couldn't check how much they were so I didn't try to buy 'em.
I'm not sure if the creator is thinking of putting in harder puzzles eventually, but with the max size being 10x10, it really isn't much of a challenge to any seasoned Picross player. A few minor annoyances to mention: the marking tool is a bit clunky to switch between that and the chisel tool. Being penalized after 'solving' a row just by going over a square accidentally is bit of a bother, but that doesn't really matter too much unless you are going for a fastest time, because there doesn't seem to be a fail state.
All in all, I am left a bit saddened, even though I didn't really invest anything seeing as it was a completely free app, the aesthetic and design of the overall app is very nice and if there were some harder puzzles, the rest of the issues could really be cast aside.