Alternately fun and frustrating
Your characters perform most actions by using skills. As a sort of replacement of the traditional "level up and get stronger" template, it puts your strengths into more specific areas, such as weaving, counter-attacking, using certain spells, etc. This way, despite a low overall level, players can excel in combat by taking advantage of high skills. The problem comes with actually obtaining and training them. In order to upgrade a skill, you have to complete certain tasks to fill up its training bar (attack an enemy with [skill], score a critical hit with [skill], etc.), which isn't too bad because it makes sense and is usually straightforward. After that, you have to spend AP only earned through leveling up. Unless you carefully plan your character, you'll have very little of it at any given time. This becomes a huge problem when you have several low skills that need to be upgraded so you can stop dying, but you'll have to be content with trying to not get hit very much until that happens.
Low skills also make item production a miserable gauntlet of frequent failure. Until they're trained to high levels, you'll have trouble creating even the simplest of items, including materials to be used in other skills. By the time you stand a chance at making a half-decent piece of clothing, you'll be so enraged by the materials lost you'll be ready to toss your needle and thread at the nearest clothing merchant.
Exploration, while a neat idea, feels limited. It is comprised almost entirely of sketching monsters and/or certain monuments, using an L-rod to find treasure like how a divining rod finds water, and accepting quests requiring you to do one of those two things. The only real benefits from this are gold and AP, if you're up to it. Sometimes it's fun, but other times it's either too easy to find the statue a short walk from the town or too hard to sketch the monster pounding your face in.
The last really notable aspect of the game is its action-strategy combat system. Simply trying to attack in a blind rage (caused by your lack of ability to tailor clothing) won't do any good - you'll have to alternate defending with attacking. If your enemy readies their smash skill, then you must lower your guard an attack them quickly. There's a long list of strategic elements here, and they separate Mabinogi from the hack-and-slash RPGs. However, this requires excellent timing, and bad moves often land you in a cycle of pain where you are unable to run away/charge defensive skills fast enough to react. I suspect (don't quote me on this) that higher-level skills charge faster, which is almost unfair considering that newbies have such a hard time getting themselves going. There's also an odd glitch where your enemy punches you from a good distance away sometimes, and there's also the threat of being ganged up on, where you're almost completely helpless alone. Combat is nice when it works. When it doesn't, it's just insulting.
Despite several large problems, Mabinogi is a decent game that some gamers will get much enjoyment out of. Although it isn't the next groundbreaking title in any sense, it does have its moments.
NOTE: In reviewing this game, I did not use any of the paid services. They might help you with combat and other things, and your gaming experience may be all the better for it.