It's picross in the browser, it is! Not much to say about it other than "good", which is actually great for a picross game, 'cos usually when I have a lot more to say, it's for negative reasons. I've only played picross type games on console/joypad, mobile/touchscreen, and with a keyboard before, never a mouse, and I can say mouse controls are now up there as being one of my favourites for picross alongside joypad controls.
There doesn't seem to be much of a proper difficulty ramp here, with the difficulty of levels being very all over the place. I'll have to try the mobile version because it looks to also reorder the existing levels alongside adding more. It's not bad, though!