For anyone who's not heard of NCSoft's latest MMO outing, its 'schtick' is that they're catering to different types of player by dividing them into classes (similar to the varieties you'd find on the Bartle test: Explorer, socialiser, killer, achiever)
While all players will experience a certain section of the game regardless of what 'class' they pick, there's a large amount of stuff that'll be unique to their chosen profession/playstyle:
Explorers will be able to find treasure troves and secret paths other classes can't find and even get missions that take them to odd and out of the way places.
Soldier class players always seems to attract trouble and so you'll stumble across battle scenarios more readily than the others, including ones specific entirely to your class. I've not been super impressed by the combat footage I've seen, though there are at least hints of having to dodge monster attacks which leaves me somewhat hopeful.
Scientists, on the other hand, get jobs and events focussed about collecting and scanning data. For those who like completionist goals, or just scanning the heck out of everything in metroid prime this class is probably for you :p
Settlers are the final class: the social one. They're all about building towns or something. Sounds interesting in theory but they've not really released any solid details on this one yet.
Art-wise/world-wise, it's got a certain charm to it and I can totally see myself playing one of those cute bunny/cat caster peoples :3