This is tough question in my opinion. Each game is different and for each game there might be a different focus...
I think that something really necessary is good criticism, you should say your thoughts while playing...like "I like this feature" or "you should improve this in that way"... Moreover often indie games are made by just one person (like mine) and in my opinion it really helps knowing if that game has potential or not...in that way one can choose to keep improving it or go on with the next project