I just received my base game and xpac. The ABSOLUTE best artwork and card quality i've seen and experienced.
I have a group to do the 4-player co-cop, but not sure where to start? In order.. base game campaign, then xpac campaign? Is reverse order possible?
Appreciate the kind remarks about the artwork!
As for the order of play, the expansion's campaign takes place immediately after the core game's campaign. Much of what occurs in the expansion will have a lot less meaning if you haven't played the core game's campaign.
If you want to play the core game's campaign with the expansion's rules and card system, you can. Should work out fine (though it may be much easier as you can gain a lot more power in the new system).
Also! Remember to keep in mind that there are side quests, called bounties, you can complete in each area (they are found at the end of each area's section within the area book!)
Hope you have fun! Feel free to post any questions. I respond pretty fast.