Online gaming exists to promote teamplay between people who generally aren't that good at People. Or something. And the best way to do this is to give everyone different, yet complimentary, skills; the traditional 'Group'. Well intentioned stuff, of course, but usually it quickly falls into the standard set of archetypes - the Required and the Tolerated.
The Required: If, when making your avatar, you stuck your pin in the list on one of these, you'll have no troubles. People will always need you, and you can pick and choose your groups. There are three essential types here:
The Tank: ('Meatshield', Warrior, Paladin, Enforcer, Knight, Brawler, etc...)
This character exists to be hit. The enemy will attempt to reduce his life points while he does the same in return. The tank has a larger amount of life points than other players, is generally better protected, and has skills to make the enemy focus on him alone. This character is the minimum requirement for a group, albiet of one.
The Healer: (Cleric, Druid, Preist, Medic, Doctor, etc...)
This character exists to replace lost the Tank's lost life points, as they are lost. Typically the spell or ability that does this, does so at a rate of more than one life point per energy point spent, effectively multiplying the Tank's available life points many times. The enemy, unless also being healed, cannot possibly match this. Attrition takes care of the rest. Tank + Healer is the basic core of a group, and in most situations is all that is ever required.
The Crowd Control:('Mezzer', Enchanter, Illusionist, Beaureaucrat, Trader, etc...)
The most optional of the Required, this character (usually fragile), has a number of implausable abilities that stun, hypnotise, subvert and otherwise control enemies. This ensures that the Tank + Healer combo have only to deal with one enemy at a time, no matter how many enemies are designed into the encounter. With these basic three, there are very few situations where attirtion and patience cannot prevail, and those that do exist have to be created specifically.
The Tolerated:Because a character creation screen with only three choices on it looks a bit daft, we present the Others; classes or professions that revolve around only one core ability or skill that didn't really fit in any of the above, or things that just sounded cool or seemed like a good idea at the time. Go away and solo, if you even can...no-one wants you unless the above positions have already been filled.
The Nuker:(Wizard, Nanotechnician, etc...)
This character is given a set of abilites that cause phenomially high damage, compared to the Tank's output, usually with a long recharge timer. However, these classes are usually made to be extremely fragile and barred from any kind of heavy-duty Tank-style protection. A shame, as even the most rudementary enemy A.I. will quickly identify them as the biggest threat and quickly beat them down. This means these classes are given a potential that far exceeds what is safe to use, in turn, meaning that for most of their life they are not fighting the game, but their own self-control.
The DPS:(Thief, Rogue, Assasin, Monk, Martial Artist, Shade, Swashbuckler, etc...)
These characters are given low damage attacks, but have a very very fast recharge on them ('Damage Per Second'); in a way, the opposit of the Nuker above. Again, they are not generally allowed to have much protection, and sometimes will have even more damage-over-time attacks; poisons, backstabing, critical hits, etc. While individual hits are minor, the sheer quantity of them soon attracts the enemy A.I.'s notice, and despite often having evasion-type skills, they are soon beaten down with no real contest. Unlike the Nuker, who can choose not to press the 'Nuke' button, the DPS's only way of slowing down their overwhelming assualt is to stop attacking altogether, or rely on hastily implemented 'don't hurt me' type skills. Again, potential far exceeds practicality.
The Pet Classes: (Creature Handler, Necromancer, Hunter, Magician, Summoner, Engineer, etc...)
This character is given the ability to either create, or subvert, creatures to do his bidding, i.e. NPC Tank. Since they usually also get an ability to heal the pet too, this effectively turns the Pet Class from one player into a two-man Tank + Healer group. Very good for soloing, so much so, that there is usually some kind of artificial xp penalty to slow them down a bit. Not that useful in groups, but then these players don't care anyway.
The Explorer: (Scout, Ranger, adventurer, etc...)
This class is given various skills that facilitate exploration of the game world; run speed, outdor invisbility, teleporting, hill climbing, water breathing, and so on. These are very good for the intended task, but rarely bring anything useful to the business of Grouping, or Winning The Game. Usually, they end up with DPS characteristics as an attempt to round them out.
The One-Buff-Wonder: (Various...)
This class has one supremely useful ability which is not actuallly needed from moment to moment, but every now and then. They have little else to offer, particularly in group combat. Examples include spells that increase regeneration, reduce downtime, increase xp/loot, travel or teleport spells, cures for longterm debuffs (diseases, etc), spells that move respawn locations, and most trade/craft/manufacturing skills. Useful people to have about, but not people you'd take on a dungeon crawl. Unfortunately, their ability is typically only gained by dungeon crawling lots.
Cool Ideas: (Various...)
Simply put, these are classes or professions based entirely on image, and not on gameplay at all. Things that just sounded cool to a concpet artist, but have no established archetype, or gameplay niche. Often drawn from one single example in a film or story, and turned into an entire profession; they may be cool, but invariably end up a botched, patched, broken class to play, as successive developers try to work out just what a 'Ninja', 'Inqusitor' or 'Trader' actually are, in game mechanic terms.
It can be a real problem though, as it isn't often immediately apparent which made-up name corresponds to what, and a player can plough weeks and months into their chosen class before realising that it is actually broken or useless.
And the solution? Well, careful design for soloability as well as group utility for a start. "Am I needed? If not, can I get by on my own?" If all else fails, the ability to transform from one to another without going back to square one. At least that way, players can vote with their feet as to whether a profession is rubbish or not.
I think mostly the way I cope with always Picking The Wrong One, is to just get on with it and grumble about it later on blogs!