Fire and Rubble will be absolutely worth it to anyone interested in the eastern front, anyone who likes CM games, and anyone who thought (like me) that CMRT was a bit light on overall content such as formations. F&R adds a ton of new equipment and formations to both sides, plus you get winter seasons to fight in. Who doesn't love some eastern front action in the snow? There really is a lot to this module, and for everyone who gets it, it will take quite a long time to make your way through all of the content. Plus, it will be great to see what the community does with it as far as new user made scenarios and campaigns go.
One (admittedly minor) benefit to pre-ordering is that you will get the game first. BFC do soft launches, which basically means the game goes live, and 12-24 hours later they make the official announcement. But if you pre-ordered, you get an email that the game is live the second it goes up. So, if you're one of those people that cannot help but comment "First!" on YouTube videos, then pre-ordering might be for you.