Most people who compare it to FFXI are not talking about FFXI in it's current state, they are referring to when FFXI was actually a fun game to play a few years ago and beyond.
Way's it is similar:
Similar races, just different names/types
That's about it.
How they differ:
FFXI had far better environments with more detail with both the big and little things. Here's a vid with scenery:
http://www.youtube.com/watch?v=iesY1XssACM
http://www.youtube.com/watch?v=kzrmwcSizIY
Combat was far more fun because it forced you to interact more and coordinate with your party members.
The story line of FFXI was better and I found it way more interesting. Not only was the original story line better, but the following 2 expansions were amazing. Obviously FFXIV can still equal as they haven't came out with expansions yet.
Traveling was more time consuming until they came out with the outpost warp, which is similar to aethryte teleporting except you paid an NPC gil rather than spent anima.
Crafting in some ways was more time consuming and tedious, but it worked differently and had additional elements that affected crafting such as moon phases.
The game was more group-oriented. In order to level beyond 20 you pretty much had to join a party, which camped and killed mobs, typically for hours. Many quests were soloable at certain levels but if you did them at the appropriate times they required you have at least 1 other person, often times 3-6. Some quests created for around level 60~ required a couple level 75 players at least, so at appropriate levels they could be somewhat difficult for players that weren't already pretty experienced.
Main scenario quests always occasionally had an instanced fight requiring you to be a part of a group. If I remember right the original story line had about 6. FFXIV's main scenario is far behind where XI's was at this stage though so it's hard to compare it properly.
Leveling was not as easily done. To get to 50 even after the cap was raised to 75 it typically took either a few months if you did not have a lvl75 and gil to support it already, or just a few weeks if you did. Being able to hit 50 in just a week wasn't possible for most people, until several years after the game came out.
All in all there is some good and bad in XI as compared to XIV. 2.0 seems very promising though and if done right could easily become a better game. I think a lot of people from XI that complain about XIV don't take the time to step back and remember they are comparing some elements of XI that weren't even out until the expansions. XI had a lot of problems itself when first released, it just wasn't quite as bad and they didn't have to take a couple years to fix the problem, they did it in stages of several months while adding good content.