I will grant that there's reason to be optimistic on this front. The director, J.J. Abrams, has made many movies that don't suck, most notably the pretty successful reboot of the Star Trek franchise. All of the original cast (aside from Alec Guinness, who did not wish to participate) will be back, playing the characters we know and love, and sure, some were a little wooden before, but it was a woodenness we came to accept.
Who among us couldn't relate to not getting to go to Tosche Station to get power converters?
But it's worth pointing out that pretty good directors and pretty good actors can still make bad movies. It happens a few hundred times a year, in fact. That might be the saddest possible outcome of all this: that the new Star Wars isn't great, nor horrible in an interesting way. It could just be mediocre.
Let's get on to the Star Wars-specific ways it could be terrible.