Easily one of my most favorite games on 360
RPGs that I've played are Super Mario RPG, Paper Mario 1/2, and Tales of Symphonia. ToS was long, and I didn't necessarily pick up the game mechanics as quickly as I would've liked, but I'm sure that my appreciation for Tales of Vesperia derives from this. ToV picked up in battle style and animation, but probably lost some points in the overall plot.
Again, if this is your first intense RPG, it'll take some time to pick things up. There are so many various aspects (altered artes and burst artes, skills, cooking) to the game that I hadn't taken advantage/known of everything until my fourth time playing.
That shows my obsession for this game. I've spent so many hours playing this that I've completed it nearly six times in the past two and a half years. One run through without sidequests could take you some fifty hours to kill. But why would you want to?
Not only did I enjoy straight up grinding and leveling up, but getting in special moves (fatal strikes, burst artes) is more than satisfying. And the multitude of sidequests is definitely an added bonus.
What I want to get across is that I wasn't always into the whole deep story, long gameplay sorts of stuff until I came across the Tales series. When I say that action adventure buffs will enjoy this, and you're into any one of the aspects of the game, give hope you'll give it a shot. I am certain that when you understand all the parameters involved in the game, you'll share my disposition.