I did the first two dungeons plus Ifirit (which is just a boss fight).
The first two dungeons were pretty simple and not difficult. There's different mechanics throughout the dungeon and boss fights have little tricks to avoid. Some of the boss fights have special mechanics you have to pull off to win - like there is one fight where you don't actually kill the boss - you have to kill adds that try to disarm a bomb while the tank kites the boss into the bomb. Some of the trash fights have mechanics also - one group of enemies I dealt with had a healer, so you had to have a dps barrel down on the healer, pull it far from the other enemy that the tank was holding, and kill each separately.
There are chests scattered throughout, but they were really *secret* as much as just randomly placed, sometimes off the beaten path.
Overall, they were all pretty fun, relatively short, easy to pug, and best of all THEY EMBRACED THE TRINITY! Thank god for that.