The good:

The initial `wow' factor is very high, as the sheer scale and level of detail of the world around the players overwhelms the senses. The art has been very carefully made, with well-animated models and magnificent special effects. Everything is designed to be immersive and for the most part, is visually polished to the nines. The audio is quite good too, with memorable battle themesand BGM for towns.
The game renders very quickly on relatively modest machines with detail all the way up (although portions of towns, such as auction houses or Bastok's Firewater Circle fountain, tend to bog down a bit).

Additionally, the crafting subsystem of the game is deep and engaging, with the ability to manufacture just about anything that NPCs sell (with the right skill level and raw materials, of course) and quite a few things that NPCs don't sell. Even low-end weaponry and armour can be recycled, which is a nice touch.

Also, care and thought appear to have been put into the economy, too
- servers keep track of how often items are sold to NPCs and the buy and sell prices fluctuate depending on their abundance or scarcity.

Finally, time of day and weather play a big part in the game's mechanics, with some monsters only being available between sunset and sunrise and some rare spawns only being available in inclement weather.

All of these combine to form a very rich and deep world to interact with.

The bad:

Unfortunately, all in Vana'diel is not perfect.

My number one complaint is that many actions simply require too much time to complete. Because the maps are so large, it is common for towns to require ten to twenty minutes of play to run across. There doesn't appear to be a `dash' or `sprint' item or spell (except that given to Thief-class characters, who have `Flee' for this). Monster combat takes far too long to resolve, with every go at a garden-variety hornet or goblin becoming a two-minute ordeal.
Additionally, the levelling is very slow, with a solo Red Mage requiring about 16 hours of play to reach level 10 (this is in Gustaberg, the desert region outside of Bastok, so the numbers may vary slightly for Windurst or San d'Oria, although all three start towns have similar `beginner' areas nearby).

The monster run speed is far too high in most cases, making it all but impossible to outrun a beastman-type monster if a player decides s/he doesn't wish to fight. Additionally, monsters will continue to chase a player for the equivalent of multiple kilometers (all the way back to zone portals, in fact).

The `Check' command frequently gives dubious information on relative enemy strength, with `seems like a decent challenge' meaning anything from `easiest experience points you'll ever get' to `I hope you like to respawn'. It also fails to take into account the possibility of criticals (indeed, the author of this article has suffered several cheap deaths from monsters that were rated `easy prey' that rolled critical hits multiple times in the same battle).

Additionally, I felt that the game was a bit too stingy and punitive at the beginning, and some things are simply horribly overpriced in ways that prevent the user from exploring too much of the world early on (900 gil health potions and 200,000 gil for an airship ticket, for example, both seem preposterous). Add to this the significant penalty for dying (10% of experience to next level up), that it takes multiple hours of play to run from one town to another and that it's possible to level down from experience losses, and the game almost seems as if it were designed to inhibit (or at least curb) wanderlust, which is contrary to the traditional aims of an adventure RPG.

The game seems to set up a bit oddly, too. The patches are very large, and will frequently take multiple hours to download and install (indeed, out of the box, it required roughly three hours of staring at progress bars before it was ready for play).
Additionally, the PlayOnline shell and addons are just annoying wastes of disk space (I already have access to email and chat, thank you, and seriously, does anyone actually ever play Tetra Master?).
Sadly, neither the shell nor the game handle Alt+Tab or losing focus gracefully, so some IM clients may cause problems.

There is no duelling, and consequently, spending the time required to beef up a character seems a bit pointless.

Finally, there is the issue of cost: at $11 USD per month, you get ONE character, where the same monthly fee or a few cents less in other games will at least allow you to have a primary character and a pack mule or two.

The verdict:

C+

Final Fantasy XI isn't a terrible game, but in my opinion, it's not exactly best-of-breed, either. The turn-based battle system and decidedly stately pace at which gameplay progresses may be enjoyable by those who like MUDs, but it is definitely not a game for the impatient. And while Square Enix does a good job of making the game `feel' engaging and immersive here, the lack of any sort of duel or player-vs.-player combat may cause the game not to hold some players'
interest for long. If it's your first MMORPG, prepare to be blown away, but users giving it a go after coming from other games may feel that it doesn't quite live up to the hype.

Ultimately, a likeable game, but for me, not likeable enough to pay for it after the introductory 30 days are up.