Burglars primarily function as a support class in LotRO, debuffing the enemy in group encounters. They can also deal a very respectable amount of damage, and are popular with some players as a solo class. I have found soloing difficult; this is a class that takes some practice to get good at, perhaps second only to the Warden.
Captains are a love/hate thing, very similar to Guardians. Their damage is mediocre at best, and their solo survivability is doubtful at times. But in a group, Captains really shine. They can provide heals and buffs, greatly improving the strength of any fellowship. If you are a group-oriented player, the Captain class is an excellent choice. If you’re more solo-oriented I’d recommend something else just because it can take so long to bring down the mobs by yourself.
Guardians are the premier tanking class in LotRO; an added benefit is the learning curve is not to steep to play this class decently (it is very important to understand threat, however, if you are playing in a fellowship). Like the Captain, Guardians can be maddening to play solo because their damage is so low; it takes a long time to take mobs out. But just like the Captain, if you like playing in a group the Guardian is an excellent addition to any fellowship, and greatly increases the survivability of the other players.
I chose a Lore Master as my first class in LotRO, and it was definitely too soon. This class has some depth, and earns its “Advanced” classification for sure! There are plenty of debuffs and crowd control skills, but they’re not much use if you don’t know when to use them. As a more experienced LotRO player I really apreciate this class, but unless you want to spend a lot of time up front learning about game mechanics, you’re probably better off choosing a more straightforward class. But let it be said that in the hands of a good player, the Lore-Master makes an excellent solo and group class.
Rune Keepers are my favorite LotRO class because of their sheer versatility. Despite being a light armor class, Rune Keepers have sufficient DPS and heals to keep them alive in most solo situations. The ability to both heal and damage makes Rune Keepers a nice addition to a fellowship. This class’ charisma is very similar to the Minstrel, so let’s cover a few of the biggest differences. The Rune-Keeper’s heals are mostly heals over time; when stacked they are plenty strong, but they require the player to plan more than for the Minstrels’ simple healing skills. My favorite trait tree (red) is damage-over-time (DoT). Once again, there is the potential for plenty of damage from these skills, but they require a little planning to get good stacking DoT. The Rune-Keeper has a unique characteristic, and that is the attunement bar. Certain skills move the attunement bar either toward healing or toward damage. The bar can go 9 units in either direction, and some of the most powerful healing skills require heavy healing attunement, and vice versa for the damage skills. The effect of this system is that the player is again forced to plan the combat skill sequence more carefully than for many of the other classes. You probably already know if you will enjoy playing this sort of class.