How far along are you Belmont? This game killed my social life this weekend. A few things have been changed slightly that end up altering the game drastically. For example:
-As Belmont said, you no longer get tired. To counter this, your HP and SP don't recover in dungeons when you leave to save. This might not seem like a big deal, but it's actually way more restrictive early game (for me at least). SP replenishing items are hard to come by (apparently throughout the whole game), and the only other option is expensive as hell. So now, instead of being artificially kicked out of the dungeon you have to decide if you want to keep on going and quite possibly die or call it quits early.
-There are more social links which auto-level, but there are also more with stat requirements to either initiate or to level up. There are also 5 stats now instead of three. As with the first game, focus on intelligence/knowledge early. You have exams a couple weeks in and a good score requires level three or higher knowledge + getting all the answers right. The bonus from this is that all your school related social links gain points if you get in the top ten.
-There is literally a shit ton more to do with your spare time, and from what I've seen all of it is useful. The side quest system is much better, fishing can get you some good items, and you will need the extra money and stats that part time jobs provide (plus they lead to new social links).
-Combat has been altered slightly and feels very different because of it. First of all, you have the option of controlling all the characters (but you don't have to). Second, analyze no longer reveals all the information on monsters, but rather just displays the info you've already discovered. Far more difficult. There is only one type of physical damage now, which kind of streamlines that whole thing. Finally, if a multi-targeted spell is cast and you manage to knock down one enemy out of however, you get another round. This means you have to be a shitload smarter defensively as an enemy or boss can just spam attacks over and over again.
I also highly suggest not using a guide. I've been reading a thread on SA on the game with some useful info, but their policy of spoiler-tagging tips has kind of lead me back into beliving that the fun of these games is making your own way and strategies (this is after I gave in on P3 and went to a fusion guide in order to improve my skills at the end). My overall strategy: Apart from items you find in the dungeons, the hermit S-link seems to be the only way to restore your SP without losing time. It's expensive as hell to do so, but gets cheaper as you go along. I'm maxing this ASAP so I can try to cut down three nights spend in dungeons down to one very very long night.
Overall, better game than Persona 3 in almost every way as far as I'm concerned.