In addition to the previous mentioned trailer there's now a gameplay trailer out there, although it's in Japanese so i at least have no idea what they're saying.
Final Fantasy 15 was originally known as Final Fantasy Versus 13 when it was announced in 2006. But development took so long they decided to make it a "real" Final Fantasy game instead i guess.
So in case you weren't keeping up with development news, the trailers make it pretty clear that it's not a turn based RPG. The combat system is very 3rd person actiony, very much like Kingdom Hearts, which makes sense given the people who have been working on it (Mr. Zipper was in charge until very recently, when he left the team to focus on Kingdom Hearts 3.) Also, aside from the 3D bit, very much like Secret of Mana.
So here's the thing. I like Secret of Mana. I like Kingdom Hearts. Those are not Final Fantasy games. If they wanted to make a side-game as part of the FF13 cluster that had action combat, that was fine with me. I'm not really happy to have this as a "mainline" numbered Final Fantasy game.
This is pretty much the same issue i had with FF12 and FF14. I don't mind the existence of the games, but i do wish they'd been titled Final Fantasy Online and Final Fantasy Online 2. I love Final Fantasy Tactics, (and think the Tactics Advance games are okay,) and i'd love to see a Final Fantasy Tactics 2. But i don't really want to see a Final Fantasy 16 using an updated Tactics engine.
I also miss the old timey fantasy/steampunk mashup art style from FF1-FF6. The more "realistic" the technology has gotten in Final Fantasy games the less i've liked it, and what little we've seen in FF15 so far looks really damn realistic. And speaking of realistic, i'm not that fond of realistic graphics either. I was perfectly happy with 2D sprites. FF7 wasn't really an improvement, but at least it was blocky enough to still look cartoony. From FF8 on the graphics have just gotten too realistic for my tastes.
So yeah, there are a lot of things making me not look forward to FF15 very much.