Shin Megami Tensei titles are always a peculiar beast. They're a grim and gritty RPG that has always been grim and gritty nearly every single entry in the series begins with the end of the world, and the picking up of the pieces. There are demons, cannibalism, death, suffering, uncaring angels, and typically a difficulty curve that will punch you in the gut if you don't prepare for it.
The Devil Survivor series is a spinoff of this, eschewing the traditional turn-based combat of the 'core' series for a more strategic form of fighting. In this series, battles are played out on a tactical grid, allowing you and your teammates to move around, find strategic positions, and take turns delivering and recieving attacks. What really separates this series from other tactics games is a number of developments.
Firstly, each 'unit' is actually a leader and two demons at their side. Only by taking out the leader can you destroy the unit, but the leader gets bonus to their defense while the other two are still alive. In addition, you get only half the experience value of the other two creatures if they're alive when the leader falls.
Secondly, selecting 'attack' from the tactical menu isn't just a matter of watching an animation play out. You're brought to a semi-turn-based mode, where each member of each team gets to attack once. If you're lucky, manage to hit a weakness, or score a critical, you may just get an 'Extra Turn', which allows you to attack once more when everyone else is done. Exploiting weaknesses and carefully managing your attacks is the key to winning these games, and if you forget this, you will fail to win the simplest battles.
And thirdly, you're on the clock. The game is broken up into events over a number of days, and anything that isn't a 'free battle' (battles for experience and macca, the game's currency) takes half an hour. There are times when you will have to choose between multiple events to the exclusion of others, and the choices you make determine what kinds of things will happen in the future, and where your allegiances may lie.
Now, Devil Survivor 2. Like most SMT games, you're a simple high school student living in Tokyo, when suddenly things go horribly, horribly wrong. Cataclysm strikes, and at the edge of death, you and your friends are given the ability to control demons, granted to you by a peculiar website that everyone has been visiting recently. As demons begin appearing across Japan, you must discover the cause of the attacks, the people you can trust, how far this calamity extends, and where a group of new, powerful creatures come from.
The story itself is pretty interesting, though people who have played through the first Devil Survivor will know most of the drill here. It takes a longer time than usual to get to the point where some actual plot begins to develop, but when it does, it gets a lot better. Mission design itself is the same as always, which means that amongst the straightforward missions, there are those where there's a very, very high chance that you are going to die if you don't already know what's coming up. This is a bad thing.
One new addition to this game over the last one is the inclusion of a sort of 'social link' mechanic, similar to what was seen in other SMT titles Persona 3 and 4. The more time you spend in events with your team members, and based on the things you say, their affinity for you will rise. As it does, they get bonuses to their fighting ability, such as being able to resist certain elements and something called a 'joint skill crack', where any skill you crack in a battle can also be cracked by them.
(For the unaware, skill cracking is how you get new skills for your human teammates in the Devil Survivor series. You must designate a skill to crack on an opponent, and kill them with the team member that the crack was designated for. Voila, new skill that anyone can equip.)
Other than that social mechanic, and the addition of some smaller ones (such as 'add-ons', which allow you to apply bonuses to newly created demon members of your team), there isn't too much new here. Sure, there are new demons abound, but if you've just come off of playing Devil Survivor Overclocked, which was just released in August of last year, there's a very strong possibility that you're going to get burned out on this game.
Worst still is that this game, technically speaking, is a step back from Overclocked, the remake of the first Devil Survivor. On the Nintendo DS (not the 3DS), it features no voice talent, a smaller resolution, and no difficulty choices; it feels lacking, especially if you've just recently finished playing Overclocked. Also, for some reason, all of the female characters in this game have some sort of gravity-defying push-up bras. I have no idea what that is about.
So in closing, if you liked the first one, you'll probably like the Devil Survivor 2 for exactly the same reasons. Though if you just finished the first one, it's easy to get bored of this one, feeling like it's just more of the same. It's fun, and well made, but after playing Devil Survivor, then playing Overclocked, it just feels like it retreads way too much territory, far too soon.