I very much enjoyed playing this game. It's well balanced and true to the lore of Lord of the Rings. The graphics are very good, as good as any of the other current generation games (trudging through late night, rain soaked Bree is particularly satisfying). The combat is good - I find the system much better than, say, Dragon Age, and nicely gory. My only criticism is that it can be a little repetitive, and it takes a while to unlock combo attacks.
I haven't played this game co-operatively and don't much plan to, but the AI is fine. If you are down they will come and revive you quickly, and they are also quick to use their powers and special attacks, which is fine by me.
I haven't completed it yet but after playing for three hours the ending is nowhere near in sight. Looking at the map there are travel locations all over middle earth so there is the promise of visiting old and familiar locations, as well as braving the less-traveled areas to the north of the map.
The tech tree is varied and comprehensive; there are plenty of weapons choices and I have been quite impressed by the way in which you can match your 'loadouts' to your playing style. Whether you like sword and shield, two-handed swords, or dual wield, the game caters for all varieties (including bows and crossbows, axes and magic attacks).
As with all games it has its problems; thus far they have not been intrusive and I have only encountered one glitch (which was quickly remedied). The side quests can be absurdly easy, and as mentioned above, the combat is a little repetitive. Be prepared for a fair bit of button mashing.
That said it's a solid game and great fun to play - you will sink a lot of man hours into it whether you're a fan of LOTR or not.