As a massive fan of Lord of the Rings, I've been looking forward to this game ever since I heard about it a few months ago. Its definitely lived up to my expectations.
As others have said, the campaigns are a bit short. However, the varying levels of difficulty help to prolong the gameplay. Most of the achievements are fairly easy to complete within the first attempt of the 'War of the Ring' and the 'Rise of Sauron' campaigns, but some require skilled online gameplay.
The ability to play as Ents and Trolls is excellent, but what puts this game in my list of favourites is the option to play as the Balrog and Sauron (finally!). They each attack with devastating effects, my favourite being the attack on the Shire. Taking down Oliphaunts Legolas-style was also a huge perk. I have to take my hat off to Pandemic Studios for adding that.
The combat system is pretty basic, but it works well in both the campaign and online. The addition of a magic class was a great touch; its my favourite for the online play.
All in all, its a great game. Obviously its not for anyone that likes to keep to Tolkien Lore. It pretty much breaks every rule in that aspect, but I think thats why I enjoy this game so much; it lets your imagination run wild. I would recommend downloading the demo first, but remember that it isnt a full representation of the final game. Try it out!