"Ugly background and ugly animations"
If the assholes told you that, they're wrong and you should ignore them. Beauty is in the eye of the beholder and calling your stuff "ugly" is a trollish non-argument. People use stock assets all the time too. Even hugely popular games do that. You have no reason to force yourself to do extra work just because some random trolls said mean things and didn't like your game.
If you really want to improve on your own terms, then it usually works better to leave the previous game alone and focus on making the new one better. But I must emphasize that this should be done on YOUR terms, not that of your internet haters.
