This is good but if you know the tricks you'll be get score continuously til you satisfied. Sorry for my bad english
If you're lucky to get a match to revert into a 1 nearby to where you previously made a match, it's possible to get a -1, 0, and 1 all adjacent to each other like three corners of a square. Once you achieve that formation, the game can go on forever as you repeatedly click the 1 in that formation and simply rotate which number is where. The adjacent tiles will go up by 1 at a time, so there is absolutely no danger of overshooting 50 or indeed any multiple of 10, and the points just keep coming in.
I enjoyed the game! It was fairly simple and ended fairly quickly (my longest game being around 3 minutes). It's definitely a game for people who like "2048" or other math-y puzzle games. Nice work.