1) Han trying to save his son from the dark side. Even the scenery had the same feel to the Emperor's little area. 2) Having to take down the shields on the planet first, before blowing up the Death Star, and Han being the one to do it. etc. etc. There's quite a few things. Just overall the feel of it was ANH + some ROTJ "sprinkled" in.
On a separate note though. I gotta say though, that final lightsaber battle was really great. They did a very good job of portraying Finn's fear and lack of skill as well as the overall amateurism of all 3 of them. Which I personally thought was good. This is essentially the beginning of an origin story. The more time that passes, the more I like the film. I'm still disappointed, don't get me wrong, and I'm sure if I saw it again I might have that disappointment reignited (or perhaps not), but once you've left the theater for a day, you start to forget all the little things that bothered you and remember the good. And there was enough good for it to be an immersive, nostalgic experience.
I am surprised at the total lack of crossguard lightsaber criticism now that the film has been released. I know a lot of fans hated it the first time they saw it and that a lot of us hoped there'd be an explanation for it, since it doesn't make sense in combat (although they did force that scene in where Kylo used it to his advantage, but still, that fucker was spinning it around like crazy, no way he wouldn't lose fingers, it's still stupid imo. But I guess everyone has looked passed that, which is fine. But there's no explanation for it. He's been trained, he has a sith master (presumably Snoke is a sith lord yeah?), so he should know how to construct one, but meh, I guess he has a specific style of combat and has found a way to make it work for him. I did like the jagged, roughness to his saber overall though.
I also like how it appears that Kylo doesn't follow the Sith playbook. He will use any force powers that benefit him, light or dark. I mean, they did mention him being on the dark side and shit a few times, which I actually wish they didn't, because it'd be cool if he was neither, but was still evil. I liked him using force push, which is almost exclusively a light jedi power. I get the sense we'll see more of that as well (hopefully), where the lines are blurred for him between light side force powers and dark side force powers.
I guess my biggest overall gripe is being really pissed and annoyed at the character inconsistency of Luke going all emo and running away. But omg the hype for seeing him kick ass will be insane. He is going to be godmode I hope. But my personal theory is that he'll be killed in the final film and that Rey will have to save the day and defeat Snoke/save Kylo. I hope to god they use that Tupac concert technology/Paul Walker shit to use Alec Guiness Obi-Wan projection and have him be in one of the next films consulting/talking with Luke.
There were PLENTY of forced lines, specially from Han. Like, are you trying to tell me that after being with Chewbacca for 40+ years that he's never used his bowcaster before? Shit like that annoyed the hell out of me.