Worth the time you're willing to spend with it.
MMORPGs are always the toughest to review - with maybe the first few hours of the game being key to determining a score. However in terms of FFXI's gameplay a few hours is not even scratching the surface of what this game has to offer. FFXI's main fault is the pacing - this game is slow. Very slow. To get an accomplished amount of things done in the game requires hours of playing at a time and for the most part, teaming up with other players. The game pretty much forces you to team up with other players in order to fight tougher monsters, leaving very little option for soloing. Unless you're with an accomplished and competant party of players, or with a group of friends, the early levels can be a chore more than a game - anyone who has been to the fabled Valkurm Dunes can tell you that. However, later on solo opportunities are increased with a quest that allows you to gain an NPC "fellowship" buddy to take along with you on your adventures. Also, being able to change jobs at any time via your moogle allows a refreshing change of pace should one job begin to lose it's appeal.
It's other main fault is the learning curve. FFXI pretty much dumps your character into his starting city (The fortress Kingdom of San D'Oria, the industrial Republic of Bastok, or the almost tribal Federation of Windurst) with little or no idea of what you want to be doing. Unless you're willing to ask questions (and find a person willing to answer) you're pretty much gonna be stuck, sword in hand, with a clueless expression scrawled upon your face. Thankfully the population of FFXI is for the most part extremely helpful with the proper attitude.
However, once you're character gains in strength, the game slowly opens up to you in terms of it's content, allowing you access to missions and quests that further the game's storyline - one just as epic and immersive as you would expect from the Final Fantasy series. More often than not a player will find themselves levelling up in order to further progress the story, which, upon after level 50 or so, branches off and intertwines with the stories and contents of the expansion packs - Rise of the Zilart and Chains of Promathia - which is when the game truly opens up. With the release of the Treasures of Aht Uhrgan expansion more casual players have been catered for with the addition of "Assault" which are small, 30 minute long missions which can be undertaken with a small group of friends - however this is only open to Levels 50 and above - a major downside to those who perhaps haven't the time to invest in levelling up that far.
As a 360 port, the game disappoints. Playing the game on a 32" widescreen TV presents a pathetic screen resolution, and horribly underpar graphics compared to those you can get on a standard PC setup. This is essentially a lazy port of the PS2 version, and only viewable at it's fullest with an HDTV setup. One the flip side however, on 360 there is much less of an issue with lag, particularly in areas such as Dynamis and Jeuno, with the game running at a constant frame rate. The soundtrack is what you'd expect from a Final Fantasy game, with a mixture of upbeat, emotional and very cool battle music, well worth picking up from iTunes.
As a game, FFXI is only worth the amount of time you're willing to spend with it. If you're a casual gamer looking for something quick to dive into, then FFXI probably isn't the game for you. If you're willing to stick it out, and want to invest the time into exploring all Vana'diel has to offer, then this is probably one of the most immersive RPGs you can get your hands on.