If I were to be honest, I didn't like the first Devil Survivor very much. The only thing I really enjoyed about it was the gameplay, and I didn't care for the characters very much except for Atsuro. The plot should have been something I would be all over, but for some reason, it didn't do it for me this time. It just kind felt like I was missing cool stuff the entire time until the last day when you choose your route. I think it's because I would have liked to see the War of Bel actually happening, which is what you can't do when the MC is also the viewpoint character of the story. Or if was more of a survival oriented thing. For the Messiah/King of Demons route, I would have liked it if there was less "become this because I think you should" and more "become this because this is what we need to do to survive." The game, I also feel, is pretty frustratingly hard. I have an Amane route run that has remained incomplete for over a year because I can't work up the motivation to get through the Belberith fight.
I have not mentioned I was playing this game, mostly because I wanted to annoy
tenshinoakuma by saying I was putting it off with no given date for when in the future I would be playing it and then just casually announce that I finished the game. But now that I have sufficiently ruffled her feathers, I can now talk about it freely!
Devil Survivor 2 pretty much stomps over the first Devil Survivor in basically every way.
All the gameplay changes made in DeSu2 were for the better. Joint Skill Cracking is the best thing. I actually only used SDTP only once, during the final boss fight, but it sure did save my ass. I love the upgraded racial skills. Free Leap saved me many times, and if there's one thing I know about SRPGs, being able to move freely around the map is one of the most valuable assets you can have (especially against those pesky bosses that have ridiculous attack ranges), making Winged Flight a godtier ability.
I am confused on whether DeSu2 is supposed to be harder or easier than DeSu1. I personally think it's easier, but it's still a challenge! It rarely took me more than three tries to get past a fight, though when I did get stuck, I got stuck pretty hard. The possessed Fumi fights were when I first really started having trouble. Maybe I'm just better at Devil Survivor this time around, but while I found some parts tough, I rarely thought they were unfairly difficult, which is a feeling I had a lot during DeSu1.
In terms of plot and characters, while the main plot I don't think is better or worse than DeSu1, but I do think DeSu2 does a better job of integrating it and making you give a damn about it. To me, characters seemed more personally motivated towards their goals. DeSu1 was more like "here's what you unlocked. Pick a route, here are the characters you get provided they have not kicked the bucket." Saving people from dying is also a lot easier, as it boils down to "don't show up late" while in DeSu1, sometimes you had to go through a complicated series of maneuvers, which can be either fun or frustrating.
I also found myself hanging out with the various characters because I wanted to see what they were up to, whereas my motivation for it in DeSu1 was usually either to advance time or open up certain routes. (For the record, the characters that ended up joining my merry little band were Daichi, Io, Joe, Keita, Airi, Jungo, Otome, and the Anguished One.) Although the characters who agree to go with you rally around the MC, I feel like they had more of an impact in each other and the plot rather than just being party members who follow you around just because, which is one gripe I have about many RPGs. The way they interact with each other and grow via the influence of other party members and not just the MC is something I really appreciated. They felt more like characters to me who interact with the environment and each other more than DeSu1's cast did, who to me, felt more like isolated entities who interact with just the MC and one or two other people.
So tl;dr, Levi liked this game would play again.