BBB - you should definitely try out the MPI and G66 maps. You can always play them by yourself, either by setting a password on your session or just not having your network setup to host games. The G66 v1.5 stuff for BZ2 v1.2 is great stuff and should definitely be experienced if you like SP/IA stuff. I am a bit biased, but that is what it is.
You can grab a very good full installer pack of G66 version 1.5 from my website:
http://www.valler.com/bz2There are even more maps out there, but that installer has everything you need to get started in one very easy file.
Centerline...