Whoever wrote the page below, has got the problem with Arcanum NPC (followers) down pat.
The NPCs in Arcanum are a very mixed blessing. They will make combat with anything of equal or lesser power to you extremely easy, for they will automatically run over and smite the enemies and deal with their own combat management. This is convenient. Even more convenient, those with healing magic (like Virgil) will automatically use it when people (like you) get wounded, and those with skills (like lockpicking) will automatically jump in and take over for you if their skill is higher than yours. Most convenient of all, they carry your stuff. I can't even imagine the annoying backpack management and constant running to the store soloing this game would entail; a friendly Sogg Mead Mug lugging your baggage around the realms is a godsend. Unfortunately, the NPCs also make combat with anything of greater power a nightmare. It is impossible to engage in tactics with them around. You can't sneak up on things; they will charge as soon as they sight an enemy. You can't draw a monster away from a group; they will charge the group. You can't get wimpier NPCs to stand behind stronger ones; they will charge to the front line. You can't get them to retreat when they're hurt; they will whine that they are about to die, but they won't flee and there's no way to tell them to. You can't coordinate an attack in any way. If you summon something, they will usually attack it and turn it hostile. (NEVER use that gem the halflings give you, for instance.) If you give them a weapon to carry or they pick one up off the ground (some NPCs are scripted to pick anything they can find up off the ground, even if it's much too heavy for them and completely worthless, so be careful breaking open chests and always dispose of rubbish in a container), they will often put away their own weapon and equip it even if it's cursed or their strength is too low to wield it. Basically, there is no way to use your superior intelligence and tactical skills against the game's AI, for your NPCs will drag you down to its level whether you like it or not. Consider it 'parity', and don't attack anything unless your guys have a clear advantage on paper.
Unfortunately, these NPCs don't have much to add to the game. Many of them have interesting backstories and quests to get them into your party, but once there, they don't do anything exhibiting a personality except occasionally comment on your critical hits and misses. Only some of them have voices, oddly enough, so some of the NPCs will speak their comments and others will only type. With the exception of Virgil, there are no special quests or quest options available if you have any of them in your party (to the best of my knowledge). Virgil, Magnus, and Raven are the only ones who ever even seem to get the occasional extra bit of dialogue. I haven't found that it matters at all to the plot which characters you take, so you can pretty much make your choices based on the kind of party type you prefer.