This is great, really nice graphics and audio. I didn't realise at first that you get more time when you catch a sheep, but once I worked it out I managed to catch 22 :). I wasn't sure if the goblins actually do anything; in fact I found them kind of helpful to lead me to the sheep. It felt like herding one sheep at a time was the best strategy, but it would have been more fun to herd more together; perhaps you could make the sheep flock together (move towards each other a bit) so that they're easier to herd in groups. Overall great game, nice work!
PS: There is no Linux build in the download, but I played the WebGL version you linked elsewhere.