I picked my copy up on Wednesday and have been slowly getting into it. I wasn't sure at first but it's shaping up to be a good one. Some observations below
There is no demon compendium that I've seen yet. In SMT games registering your demons in the compendium meant you could buy them back after losing them in fusions.
Update: Found the compendium. You need to go to a specific location to access it
Overuse of fusion can result in your demons dying on you as you walk around. At least that's what I deduced. At first I thought I'd been poisoned. You get that flashing of the screen as you move. Then I realized that one of my demons had been removed from my party because it was dead. The others were in various states of HP loss.
Update: The above is wrong. You have a finite amount of magnetite which reduces as you walk around and is gained when you battle demons. If you let it go to 0 your demons start to die.
I've also heard that demons will bugger off on you if you don't treat them right. That should be interesting
You can use the coins you collect while your 3DS is in sleep mode to buy D-Souls which allow you to buy demons from Nemeichi. You can't buy infinite D-Souls though. It cuts you off if you try to go nuts which I did. (Big surprise! LOL)
The game doesn't handhold you at all. There aren't as many tutorials.
Update: I forgot to mention that unlike other games your demons do not level up or learn new abilities.
So regardless of the original games age I think this one's going to be another positive SMT experience.
I like the whole "hacker angle" even if many dungeon crawls are too intense for me now days. So, Demons take damage as you walk? Hmmm, don't know how I feel about that. I suppose it could add an interesting wrinkle of strategy and resorce management.
I think my demons were taking damage because I was overusing fusion or something like that. They didn't start doing that until I bought a bunch of demons with my coins and started fusing them like a man possessed.
You must have morals with your science,Peter! (In retrospect that doesn't sound fun at all! Never mind,keep going with the Frankenstein approach! Deaths 4 progress!)
It sounds like it might take some time to get use to this game.
I just found out that my demons are dying because I'm running out of magnetite. I guess I'm not supposed to have 4 demons at once or something like that. I also keep reading about hacks in the game that allow you to change the difficulty and other stuff but I haven't seen anything of the sort so far. It doesn't help that the manual is a piece of crap.
Sounds like a good game! I'll eventually be getting myself a copy!
Like most MegaTen games, I think this sounds pretty cool and I hope to get it sometime. But like most MegaTen games, I'll be lucky if I do 
Everything about this makes me not want to try it out. Which of course means I will buy it an throw my 3DS against the wall if it gets hard. Have you read my impression of Fire Emblem? Yeah. Exactly.
I'm still deeply embedded in Etrian Odyssey, and my brother just got the newest Pokemon Mystery Dungeon so there goes getting him to buy a copy. Looks like I'll just have to bite the bullet and see if I have the funds to get a copy.
Update: Nice to see you are enjoying it.
I came very close to buying it on vacation. Saw it at Fry's while I was in there. Gonna need to devote some time to it I think. That is always the tricky part for me,but may pull it off.