Where I think it excels most is the sheer variety of gameplay on offer and how you can change at any time you want, while carrying over some abilities and augments from other vocations. But why it excels here is represented by the abilities in general and how well they define their respective vocation. Simply put, Dragon's Dogma without question has some of the most badass abilities I have seen in the action/RPG genre.
Then of course you have to factor in all of the little things that enhance the gameplay, such as how enemies start to bruise, bleed and show damage, how the flesh starts to burn off of them when they catch fire, how you can get soaked and it extinguishes your lantern, the use of night/darkness in general, climbing enemies, the platforming aspects, etc. Weigh all of that together, and you have something that is quite unlike anything else out there.
Indeed, it's already an amazing game because of all of these factors combined, now just imagine where it can go from such a foundation. Pretty exciting to think about.