Personally I don't think it's worth it if you don't intend to play multiplayer.
At the moment the AI is pretty lacking, but as with most RTS games, pretty much anything you can do online, you can also do offline with computer players. (You're limited to 4 player maps though for some reason, which you can get around by hosting your own multiplayer game and adding computers to fill in the rest of the slots.)
Personally I like Battle for middle earth 2 better, it's lacking in AI as well, but there's so much to do in there, and the 3 vs 1 maps (you put a brutal computer at the fortress to defend and you have 2 AI allies) are excellent. Just be sure to put the AI players on "brutal" or else it's no challenge at all.