The main concerns I had in advance can be summed up in a comment I left on Gamers Decrypted when Noctua posted about the release of the trailer back in October:
I liked it overall, but I was a bit taken aback and worried by just how many parallels to Episode 4 there are. Evil Empire vs. scrappy rebels, mysterious bad guy with a mask leading the charge, young person who has the force but seems to not know how to use it, events of the past have been forgotten or are treated as myth etc. There is pleasing the fans with references to the original, and then there’s doing a full retelling of the old story with a new coat of paint.
In reality there were indeed a lot of parallels to A New Hope, but at the same time the new story and new characters brought enough freshness to the table that I never felt like there was too much pandering to nostalgia going on.
Rey, a fantastic new character. Image courtesy of Wookieepedia.
The key is that the film managed to hit all the right notes throughout, from well-placed funny lines to tear-jerker moments to times when you'd gasp in excitement or shock. The classic good vs. evil theme is present but is also immediately treated with the sort of nuance that we didn't actually see in the original trilogy until quite late. As a woman I also found myself nearly squeeing with delight at the improved treatment of female characters compared to both of the previous trilogies. There are details you can pick apart and criticise of course, but they are all of the type that might come to mind when you're dissecting the film in conversation with your friends afterwards, not things that detract from the story while you're watching it.
The ending leaves a lot of open questions which immediately made me look up the proposed release date for Episode VIII. (It's May 2017 - so far away!)
On a side note, it's worth noting that the ads before the main feature advertised three or four video games, but not one of them was actually Star Wars related... what a wasted opportunity.