I can't choose only one thing so I will try not make it long.
What I like:
Game is based on Dungeons system and I love Dungeons. I like the sync system as well.
The story. Perhaps the only MMORPG with actual plot, good cutscenes and voice acting.
Community. One of the friendliest and non toxic EVER period.
Technically a well done and optimized game. It runs very well in all systems and scales performance nicely. Also one of MMORPGs with the fewest bugs and glitches.
Job system. You can have all jobs with one character. No more scratching head to find names for alts and lose time switching between them.
What I don't like
Poor end game content. Not much things to do once you get the gear and you get the gear pretty fast. And I play few hours per day. Not many things to engage the long term players.
Poor character customization. (I do not mean the glamours but the character creation screen. very poor and too few options. Everyone looks like each other.)
Crafting requires too much money for no actual rewards. I mean it's only for glamours and furniture. Once you get your house and decorate it crafting is useless. No good weapon and gear from crafting that can replace long term the tomestone ones. Crafting is not necessary in game it's more like a time/gil sink.
Class system utterly useless. We should have Jobs only from the beginning.
Maps feel kinda small. Not too small but smaller in comparison to other MMORPGs.
No open world content.
PvP is not well done and it's rather poor in this game.
The things I like outweight the things I dislike. The game has a lot of potential and many things to change and improve for sure. I have great expectations from FFXIV and I do hope to see this game grow much more.