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In terms of game features, I think Mabinogi would actually appeal to many MMORPG-fans -- it has many of the things players always seem to ask for in their games (housing, player shops, combat pets, gear customization, RP tools, etc). For people who hate traveling, crafting, 'playing dress-up', anime, or any hint of grind-y stuff, it may not be that appealing. There is a strategy to efficiently skilling up your character and succeeding in combat, but for people who are used to have 20+ different kinds of flashy attacks to choose from with tons of mathematical calculations for min/maxing them all, the simplicity may be hard to transition to (though I actually found it kind of refreshing, plus it allows you to kill things higher level than you with the right skills). There is also voluntary PvP and an Arena, though I don't know how popular they are.
After learning about the different races, I would have to strongly recommend that people make a HUMAN for their first character. Human players get a free Elf or Giant character slot once they ally with one of those races, whereas people who start out as one of those two would have to pay for a second character slot. Humans are very balanced stat-wise, which makes them a benefit for beginners (they are also the only race that can dual-wield bladed weapons, which I know lots of people like). Also, only Humans can do the storyline quests at the moment (future patches will introduce storyline quests for everyone).
If you are someone who likes skill-based MMORPGs with lots of crafting/socializing/soloing options, Mabinogi might be right up your alley. If anything, it's worth laying aside any preconceived biases you may have against F2P MMOs just to try it out for a few days... I know I was pleasantly surprised by how much I ended up enjoying it. If you really want to, you can even choose to pay a $9 or $15 monthly fee for extra perks, although it is perfectly feasible to play free (perhaps only buying a mount or other one-time cost items here and there) for as long as you want. The game gets content updates about every 6 months or so, and new items added to the cash shop randomly.
Feel free to look me up on the 'Mari' server if you're ever trying out the game and need a free ride around newbieville. =)