Is this forum the only active community about IC2? The IRC channel didn't have any messages for a few hours I was joined and even this forum has pretty low activity.
I consider this forum "active". It's just a slow activity, like responses in days, not hours.
There are few developers, so you won't see 1-2 day turn around on ideas / suggestions. Therefore there is not a vibrant community suggestion forum, but you can say something and you will get responses.
Because the mood doesn't change daily or weekly, there are not a constant stream of bugs. Therefore there are not a vibrant but community, but you can say something and you will get responses.
There are something like 10-20 "regulars", including developers, and I've never seen the forums completely dead.