Like the first "Battle for Middle-Earth" game, this is one my favourite RTSes. Again, you can play on either the "Good" or "Evil" side, but this time your choices are expanded to play as Humans, Dwarves, Elves, Goblins, Orthanc (where Saruman lives) or Mordor. It's a fun, high-energy game in any case.
The first game follows the movies pretty closely. The second tells the story of what happens while the Fellowship is away on their quest.
What made this game unforgettable for me were not only the battles (which are awesome!), but also the fact that you can play a "Risk"-style campaign across Middle-Earth, where you strive to take your opponent's capital (e.g. Orthanc, Mordor, The Shire etc.) You can also play "Skirmish"-style battles, where you not only fight your opponents, but also -- if you're lucky enough to find and slay Gollum -- you can command the One Ring to summon special allies. (I won't spoil it). :-)
I would also recommend the expansion, "The Rise of the Witch-King", which tells the story of the Witch-King of Angmar and his rise to power. (If you remember the films, the Witch-King fights Gandalf at Minas Tirith and ends up killing Theoden, only to be slain by Eowyn and Merry, at the Battle of the Pelennor Fields). But where did he come from, and what did he do? This expansion answers that, and a lot more.
Like the first game, this is an awesome RTS, full of action and planning, and very immersive too. Two thumbs up, way up!