I've played quite a few PBEM campaigns.
Many years ago, when I switched from playing against the AI to human opponents, I could never really go back to the AI. Human opponents are just a lot more fun. But I missed the campaigns.
Now with PBEM campaigns...well, it's just the next level of addiction.
PBEM camps are not much different to a series of PBEM battles, where you get to decide or negotiate the circumstances, maps, v-hexes, preferences etc. for each battle. But there's continuity with your core, and you get to know your officers, or hopefully they are around long enough to become familiar.
My only complaint is that the winner is awarded a lot more repair points than the loser (often double). This makes the next battle even easier for the winner, and the campaign can soon become unbalanced.
This unbalance quickly 'snow balls' and has caused a premature end to most of my campaigns.
I actually think the loser should be getting more repair points. He's likely the less experienced player, and he probably has more to repair, so he's the one who needs help if he's going to have a chance at a successful second battle.
To combat this problem, I recommend keeping the turns low (15 to 20, but I may experiment with around 12) which will help keep battalions from being decimated.
Apart from that, you could agree that the winner is not allowed to expand his core. I volunteered to do this, and it helps.
cheers,
Cross