My group just finished the second module... but I have read/prepped out to module 6.
Things I really like about the arc:
- Detailed campaign backstory.. it answers the 'why' of the plot-lines
- Story driven, many of the modules have a portion of 'what if...' where the authors look at the impact of possible endings. For example, If the PC's fail to capture the Case in module #1, the storyline doesn't fall apart.
- Setting Generic. You can fit the story into many published settings with little effort. I am running the game in the Eberron world.
- Many encounters have options for non-combat resolutions.
Things I don't like about the arc:
- My group only plays once a month, so despite having read/preped through #... we are starting #3...
{Oh wait, thats an issue with my groups schedule

}
But seriously, I am very much enjoying the game and think the campaign is one of the better designed ones out there.