If you just want to play more FS2 missions (I know that's the way I feel sometimes

), I would suggest:
The Aeos Affair - very difficult 10-mission campaign, by Picklehead. Might be my favourite complete FS2 campaign of all so far. If you can complete it on Insane, come and tell me - you'll be the only other one I've met aside from myself.

Link:
http://freespace.volitionwatch.com/aeosaffair/Aeos-Affair.zipWarzone - fantastic 19-mission campaign, by IceFire. You shouldn't go by without having played this one.
Link:
http://www.3ddownloads.com/?file_id=97318And then there's Derelict, which ought to be on the Archives, I think, which means you've probably already played it.

Don't know why I picked out these 'old' campaigns, I suddenly had this nostalgic feeling of what it was like to get out of FS2 for the first time and then want... more FS2.

Hope you enjoy those!