The game is clearly based on the same engine, but I don't know what else you could possibly have expected. I'll admit that the AI in VC2 was pretty dumb, but other than that what 'mechanical improvements' do you want? Story aside, VC2's gameplay was fantastic. Better than the first game in my opinion, other than the small map size anyway. Which is something they have actually claimed they're improving for VC3.
From what we know so far the story already sounds more promising than VC2's.
BTW, the demo is already out on the JP PSN. You don't have to rely on gameplay videos.
Mechanically I'm referring to everything that happened outside of battle. Aside from the AI I'll agree the battle system itself is pretty solid. That's what got me through as far into the game I got before quitting. The rest of it though...really needs serious refinement/re-imagining. I'll try and highlight the major issues so I don't have a huge list of nitpicks.
-The Social Development Aspect: Mechanically this element detracted from the gameplay value in terms of how it was presented. The idea of "socializing with your team mates in order to advance their powers by overcoming their social faults" has been done better, with of course the prime example being Persona. The philosophy presented behind it is where the SDA falls flat. For comparison:
Persona: Let's socialize with my team mates at regular intervals to learn more about them and gain some powerful bonuses gradually so they'll be more effective in combat.
VC II: Let's socialize with my team mates at random intervals in order to keep them from absolutely sucking
The part I bolded is the key point. The "flaws" your team can have in VC II ranged from minor annoyances to making the characters outright unplayable if the fates decided to screw you. Nothing like selecting a character only to have this happen: *one step* *two step* OMG! I'm having an irrelevant mental crisis! *character is unable to move anymore*. A mechanical change is needed to make the characters have lesser flaws while gaining more powers at a slower rate. (Extending the "stories" for each character from 4 to 6 scenes and having a "Potential" awaken every 2 scenes would be a nice balance, for example.)
-The "Currency" & Level Up System: The funds you use to buy gear with in VC II were way too plentiful. Every time a chapter rolled around I found it way too easy to purchase everything and still had funds left over. Not to mention most of the purchases on the "tech tree" were pretty useless IMO. With a few exceptions the best option was just to go straight down and when it did offer alternate purchases it was usually only one other choice for one or two classes per chapter. Not even the Tank purchases felt relevant aside from "personal taste". Just equip a AA turret with a AP secondary and everything dies unless they have God-Mode evade turned on (like certain bosses). VC III would need more branches on their "tree" with more relevant choices that make me want to buy something besides the "standard" gear.
Also the Level Up system felt unnecessary. I think I got up to level 15 or 16 in all my classes and honestly I didn't feel more powerful than I did at level 1 aside from a larger HP pool. Enemies still took the same # of hits, I still died with the same # of hits...why give the player levels if they feel empty? The only time I felt power boosts were during Class Changes. The Class Changes themselves were decent but that system is also flawed. I don't mind having to farm items for class changes. But two things drag the system down:
1. Needing to restock the medals to change into a class you've already unlocked. Look at a game like Final Fantasy Tactics. Do I need to re-level a Squire to Lv. 3 each time I want to change into a Knight? No. There's no reason to. It's just silly game padding to extend the length via useless farming. This even wouldn't be so bad except...
2. The items needed for Class Changes are rewarded randomly. I remember much frustration of making a certain character try to solo a map, only to have them not get the items they needed because the character who weakened one random soldier to let the other character get the kill got the Certification...somehow. ~.~
I could go on and on but I think those two things reflect the major changes VC III would need to the non-combat segments of the game. There are other things but I consider them minor.