>High quality assets is orthogonal to fun.
Not necessarily. It's a very "programmer brain" thing to think that novel mechanics are the be-all end-all of what makes a fun game. Extremely simple games can become incredibly engaging given high quality detailed beautiful art design. Think of deck builders and board games that would be pointless with just placeholder images and spreadsheets of data, that actually become enjoyable because of the creative work that went into the assets.
Not what I was saying. You can focus on assets once you nailed down the game design aspects. You can have beautiful assets and a bad game the people do not enjoy (so many AAA flops), but they will forgive not so great assets if you have a fun game (a lot of indie game).