Battle for Middle Earth II is far from your average RTS game, but it's certainly not perfect. You'll play it over and over, but some things get in the way of this becoming an amazing game. Despite these things, I recommend that you pick it up if you can. It's well worth it.
The maps in this game are not too varied. Yes, they're all different, but most of them give you the same symmetrical, 2v2 feel (this does not promote teamwork at all because it takes time to send your troops there and back, and if the other team has good communication they will easily defeat you). This isn't a problem however, because if you get bored of those maps after a while, you can either create your own using the map editor that comes with the game, or you can simply play maps created by others. Some of the maps you find are extremely fun and creative, from hero only maps that recreate the storyline of the book to tower defense modes. Essentially, custom games will keep you occupied for countless hours.
Heroes are a great angle that adds an extra degree of strategy to gameplay. Because each hero is different and has a different cost, using them can make or break a match. If the host allows it, you can also use custom heroes that you create in the custom hero menu. The problem there is that custom heroes are EXTREMELY overpowered. Their powers are better and quicker than all the other heroes for cheaper than quite a few of the default heroes. Another imbalance is that different armies have more or less heroes. This may be done to balance out armies, but it seems like it wasn't done well enough, so that if the game gets to the point that you have all the heroes and a massive army, often the person with more heroes will win.
You always have the choice of playing as either men, elves, dwarves, goblins, isengard, or mordor. Obviously all the armies have different pros and cons, but some armies seem to have more cons than pros. For instance, it's impossible for a player using goblins to defeat a player using dwarves. The goblins have speed, the dwarves strength, and unfortunately the dwarves will win within minutes. This just means that you will normally only be able to play as armies other than goblins. In general, the good armies seem stronger than evil ones, although a good player will be able to win with either side. The only time this becomes a big problem is in a goblin vs dwarves scenario or if there is a large (10 to 16 people) party where there is a large discrepancy in the ratio of good/evil armies on either side. Otherwise the overpowering seems rather mediocre.
Playing team matches is really fun online. The use of powers can sway a battle, from spying on your enemy to raining down a meteor shower on their units and buildings, just like good communication can. Every match is different, and you develop strategies over time that tend to work more often than not, and the game only seems to get more fun. One big problem, however, which may have been my connection or the fact that I'm in Canada, is that finding a suitable match was really difficult. Not because there wasn't a match with a map or game type that I like, but because I could never seem to connect to people. Now my connection is definitely not as good as most people, but I think the system is too harsh for letting people play together. Surprising, considering the graphics definitely aren't superb. I'm sure most people won't have this problem, but it's something I encountered worth mentioning. All online games have problems, and this is just another of them.
Basically, a great RTS game that has very good replay value and a unique gameplay. Moderate balance issues and online connectivity problems prevent this game from reaching it's full potential. A recommended buy, however if your internet connection isn't very good, you may want to shy away from purchasing this one.