Mabinogi is...different.
Like it was said, its very anime-ish, but also quite fun.
Character creation is simple, for the most part, and aside from a "focus" you get when creating your character, there really isnt a job system. Said focus is either warrior, mage, or ranged, with each focus doubling the rate at which you improve skills related to melee/magic/ranged
There are a ton of skills. some are useful, some not quite so useful, but there there anyways. want to make your own armor? you can go out, mine, smelt the ore you get, and craft your armor. itll take a while, but it can happen. want to be a mage? theres a ton of spells (including awesome spells like ice spear and fireball. thunder is especially nice). want to be an alchemist and use a flamethrower/water cannon while summoning a golem to fight with? you can do it. however, being a pure mage is rather hard, due to mana regenerating slowly. but theres potions and weapon mods for that.
whenever you level a skill, it boosts your stats in addition to its getting stronger. this applies to both combat and non-combat skills. in fact, in order to get better at what they do, youll often find that swordsmen are also blacksmiths/tailors, while mages have some skill at herbalism and other skills.
As for aging, you get to choose from age 10-17 when starting. every saturday you age 1 year, up to pretty much infinite. when you age you get status bonuses, as well as AP (which is used to level up skills), until you turn 25. When you hit age 20 (maybe 21) you can rebirth your character for free.
Rebirthing basically resets your characters AGE, LOOKS, and LEVEL. skills/stats are affected as well, but only the points you gained from aging are affected. points/stats gained from trained skills, however, still affect you. so, essentially, you gradually get stronger and stronger as you train, even if youre just rebirthed.
as for the story, its actually pretty good. get a little creepy sometimes when you log in and BAM, cutscene, but otherwise its not bad. In fact, some of the best loot can be gotten from doing story missions. after doing generation 2 of the story, you get to transform into a Paladin, which gives a MASSIVE boost to your stats, as well as looks cool. after playing generation 3, you can turn into a dark knight, which has different skills, at the cost of never being able to transform into a paladin again. Thankfully, you can skip the story if you want, and still be able to transform, but the quest to get the transformations is a LOT harder than if you had just gone through the storyline
As a korean MMO, mabinogi can be a little grind-y. however, given that you can pretty much do whatever you want, the only stuff you grind for is the stuff that you already WANT to grind for, instead of stuff you HAVE to. Levels go surprisingly fast, and theres even a secondary leveling system (sort of) that gives you levels for finding/sketching artifacts and creatures, and doing special quests. combat, while being solo-able, is often very fast, very harsh, and quite unforgiving. if you tangle with something that you dont know how to kill, you WILL be taken out. that said, its also fun when you level up a skill enough to just blast through the enemies that were previously taking you out, although they still can if you get lax (goblins, im looking at you)
As for the community, it can be bad at times. however, it can also be quite good. its just a matter of who you find and when, really. and its always fun to see 100+ people gather for an event and basically tank through everything
overall, id say that, while it can be quite frustrating, it can also be quite rewarding. if youre looking for an mmo where you can be whatever you want to be, while also exploring/gatherring/just muckin about then you might want to try mabinogi