TFC is fun to play, but it changes so much that it even changes the world gen. A lot.
Based on this, I am not sure if other mods, like RedPower, could add their own stuff.
Also, I never found a single NPC village in TFC, and as far as I know, the whole treasure chests is completely different, so some mods like Mystcraft would compatibility have problems (read "would not crash, but would not work either").
That said, I really encourage anyone that didn't know about it to give it a try.
It is hard, and the first few days really focus on survival, scavenging for food and not having a proper place to hide at night.
At least, it makes it very difficult to even envision digging on your first day, and even cutting a tree needs a tool.
The bad part is that you basically need to have a guide open on the side, to know what to do, but that's a fun experience nonetheless.