I played both and basically hate both for different reasons, so this sounds right up my alley!
First, FFXI. This game is extremely party oriented, so much that you can’t really progress beyond level 10 without a party (unless you’re a beastmaster, which is pretty much the solo class. Other classes can have SOME success but it’s really just an uphill battle.), because of how exp is calculated and how terribly punishing the monsters are. The combat is pretty much just positioning yourself (outside of monster AoE range, don’t walk into another party, etc) and selecting attacks through a text interface (macros and keybinds are possible). You have hp, mp, and tp. The first two should be obvious, tp is a bit different. It starts at 0% and can build up to 300%. The more you hit with physical attacks and the more you get hit it builds up. Once it hits 100% you can unleash a weapon tech, which kind depends on what weapon you’ve got and your skill in that particular weapon. This is a fun party dynamic, as multiple weapon techs can be strung together for combos, with the mages being able to “magic burst” for increased damage. Other than that, the combat is pretty much what you’d expect, except incredibly punishing. There’s also a pretty heavy exp loss on death, which can be somewhat remedied by getting raised by a friendly player.
Depending on your job and subjob (you can set a secondary class which is capped at half your level, providing minor stat boosts and access to extra abilities) your stats are calculated. This is just generic stuff like hp, mp, str, int, etc. Alongside your stats you also have skills. The more you use, say, great axes, your great axe skill increases. This is capped by your job level, and if your job or subjob doesn’t give access to a certain skill you can’t use that type of weapon or magic. Skill affects everything from potency to accuracy.
After level 10 you basically spend ALL YOUR TIME trying to get a party together. This isn’t so bad if you’re a caster, since they’re very wanted, but pretty much every melee class is fucked, with longass wait times. I’m talking hours, sometimes days. Then you’ve got a party and you basically just go kill random shit until you level up. The time it takes increases as you get higher in level, and you really need to be able to dedicate several hours at once to get a meaningful session going, and not piss off your party members. Endgame basically is either leveling another job, doing more quests or missions (there are a fucking LOT. Seriously.) and fighting huge fucking monsters with your guild and teaming up with other guilds to do crazy fucking holy shit is that a level 2 million RANDOM SPAWN MOB we’re only 80 level 75 guy–gah I’m dead things. Long story short, there’s plenty to do.
There’s also quests and missions. They’re pretty much what you expect, though a good deal of (low-level) quests can be soloed, and they tend to give items as rewards. No exp is given for quest or mission completion, by the way. Missions are basically huge fucking quests that dish out plot, which is actually fairly interesting. They generally don’t give rewards, besides an increase in your nation’s rank, which has it’s own rewards (access to certain items, airship access, etc). Among these are a lot of special events, such as Garrison (take your guild, defend NPCs from zerg rush), BCNMs (special capped fights that tend to give great rewards) and some new fangled exp quest dealie. There’s quite a lot to do, and most of it is pretty interesting. You can also decorate your own house, but because S-E is retarded you can’t invite people into it. There’s also crafting, which is mostly a money sink and frustration. You can make some useful stuff and good money at high levels, though, and you can get pimping golden shades.
You can be a citizen of one of three nations; San d’Oria (racist militaristic elves), Bastok (communist humans and a repressed black working population) and Windurst (magical midgets and whores). You can change nations at any time (for a cost). As you go around killing stuff your nation might control a certain region one week, or lose control of a region. This affects the items that are available to you, respawn points, teleport costs, etc. It also affects what missions are available to you, since there’s a distinct plot for every nation (and plot for all expansions). The plot is unique since it’s pretty good. For an MMO, but still.
The graphics are kind of generic fantasy stuff, there’s no voice acting, and the music is decent but seriously nothing you want to listen to for extended periods of time. Since you’ll be spending a LOT of time listening to it.
The economy is retarded, and as such you tend to have to work to earn the money necessary for gear upgrades. As in, crafting, or mining, or farming, or camping Notorious Monsters and hoping they drop items worth tons of gil only to have the spawns get stolen by chinese gilsellers.
In short, FFXI is fucking hardcore, requires a HUGE time dedication, and will have you piss blood.
Now for WoW.
You’ve played it so I don’t really need to give too much detail. Basically, WoW is everything FFXI isn’t. Unique graphical style, casual gameplay which facilitates soloing, no real death penalty, and it has PvP. However, it has shit for content. It is very possible to see all there is to see in a few weeks (or a few months, depending on how much you play) and once you reach endgame there is no more casual play, just rape and murder of the same goddamn instances over and over again. It’s also really, really easy. Then there’s PvP, which is flawed on a very basic level in that it rewards time invested into it instead of skill and has a HUGE slippery slope, and since classes aren’t balanced for one on one combat (why? why?) there is no real competetive gameplay to get from it. Unless you count battlegrounds, which is a joke.
However, it’s got a streamlined interface, no stupid grinding for money (mostly) or exp since everything is quest driven, crafting that doesn’t require you to spend 20000 hours making the same recipe hoping to get a skillup (though as a result is mostly worthless), and /train.
In short, WoW is fucking retarded, requires no time dedication, and will have you cry tears of blood.