Skills are your best friends, but be prepared to use them all the time and repeatedly; you only gain one skill point per attack.
In addition to their normal attacks, your party members will all have access to two different sets of skills. One set is usually based on the weapon that character uses (sword skills, spear skills, axe skills, and the like), and the other set is generally magical in nature. You level up your abilities by using them. Each time you use an ability from a particular "tree," you'll get a point in that tree. Earning the best abilities takes quite a bit of time, as you only get one skill point per use of a skill, and you'll need to focus hundreds of points in some trees. The patient will end up with an arsenal of abilities that include multiple attacks in a single turn, stunning monsters and putting them to sleep, as well as healing your whole party, raising your group's defense and evade rate, and so on. And when you level your characters up, you'll be able to allot points to different base stats, like strength, speed, dexterity, spirit, and so on, so you can customize on a few different levels.
The system works well on the whole, though investing in abilities gets to be time consuming at higher levels. The special powers at least generally look great, with lots of shining swords held aloft and dramatic creaking of bowstrings, but there's only so much variation in them, and you're going to be seeing some of them hundreds and hundreds of times as you patiently raise your points in increments of one. The bulk of the powers are fairly short, but there's no way to skip the special-effects show manually. In addition, some of the effects seem to act oddly. It's possible for an enemy to register as immune to a stun, but then the enemy will appear stunned, drop off the list of action portraits--and then still be able to move normally. Also, some of the enemies have special abilities that will slow your turn or decrease your attack strength, but there are no icons onscreen to show you this. Sometimes you'll just be left guessing what exactly an enemy curse just did to you.
When you complete a chapter of the game, you unlock "evil mode" for the chapter cleared. While this sounds very interesting, evil mode is actually just a selection of battles from that chapter, generally around five or less, that you'll fight from the side of the Mordor forces. They're usually very quick to go through. You'll be plunged right into the next battle upon a victory, and you're not done until you've cleared all the fights, and when this happens, you get a handful of items. Usually there's a nice weapon or two thrown in that will likely be better than what you have equipped, so breezing through the mode is usually worth the trouble. It's just not terribly interesting--unless you're playing the fight as the balrog, because as we all know, huge fire-demons are awesome.
Visually, the level of detail and care that went into the various characters--and even the enemies--is great. Each of the many, many pieces of armor and weapons that you'll find along your journey is distinct and uniquely designed. Polished steel shines on Berethor, leather clothing rumples naturally on Elegost the ranger, and Hadhod the dwarf looks best in mithril and velvets pulled from the crypts of Moria. The characters themselves also look very good, and the motion-capture technology employed for their animations is mostly to good effect. There are still certain animations that look a bit wooden, but those aren't too bothersome in the face of other eye candy, like the now-ubiquitous "bloom" effect that accentuates the special effects in the game. The Xbox handles all the white-hot wizard spells, shining weapons, and multiple shifting characters a bit better than the PS2 does. Both versions of the game are prone to a bit of slowdown, but in the PS2 version it's very noticeable and it can be a little on the disruptive side, particularly if you're fighting someone that's graphics-intensive, like the fiery, smoke-billowing balrog.
Insofar as music goes, if you appreciated the grand scores of The Lord of the Rings films, then you'll continue to appreciate them here; the music for the game is straight from the movies. The stirring orchestral and choral themes for the various characters and locales really serve to root you firmly in the Middle-earth experience. The voice acting is also excellent; Ian McKellan brings the same richness and nobility to the voice of Gandalf that he brought to the feature films, and the rest of the cast is also of very good quality. Again, it's a shame there isn't more original interaction between the characters in the game, as their dialogue fits the milieu perfectly as it's written, and it's acted just as well. All the sound effects in the game are excellent, from the gurgling of the uruk'hai to the clear ringing of steel blades held aloft to the subtle clinking of your armor and scuffing of pebbles and dirt as you run. The only slightly jarring note in the sound package is that some of the other characters you meet will speak in what is obviously recycled movie dialogue that has been repurposed for a slightly different scene, and it sounds out of place.
Want to go back to Middle-earth? It can be worth it.
Even with all the skill-raising and orc-hewing, the game takes about 25 hours to finish if you rush, and 30 or longer if you want to take your sweet time and gather up skills. Otherwise, it's pretty easy to get 100-percent quest completion on all the chapters, and there aren't any extra features unlocked when you beat the game. There is a co-op mode, but it's poorly implemented; it consists of someone plugging in a second controller and then selecting an option from the in-game menu. Player one controls the movement in adventure mode, and the two players trade off controlling characters in battles. As multiplayer in a turn-based game, it's just not a whole lot of fun. You're better off just leaning over your friend's shoulder and telling him or her which ability to use.
The Lord of the Rings, The Third Age molds Middle-earth into a traditional turn-based frame, and while the results aren't all that great, the game carries some pretty good features and should appeal to fans of the source material.