Well there are many reasons basically though there just poorly made films,now the original trilogy was no artistic masterpiece but they were well made,followed the heroes journey to a T,visually pleasing full of memorable characters.I'm still not sure who the main character suppose to be in the new trilogy the plot is so unnecessarily convoluted with cringe worthy dialogue to boot and no memorable characters other than the ones your already familiar with, BECAUSE THEY KILLED ALL OF THE ONES THAT WERE REMOTELY ENJOYABLE!I think the creators immediately put themselves in the hole by making it a prequel trilogy and maybe not just one movie but I'm sure mostly financial reasons helped motivate that decision.
The thing that sucks the most for me is that there are small bits and pieces of that magic scattered amongst the three movies that made the the original trilogy so enjoyable for me.While I don't hate the new trilogy as much as some I hate the fact that it was a wasted opportunity for the Star Wars universe because it deserved more than the mediocre treatment that it received.
At least modern technology helped make the action super fast and sexy.Without that I see no other redeeming quality of those movies.The bright side is that there are still other outlets for solid Star Wars experiences,books,games,etc.