Well, I completed the game as every class, with the condition that I cannot return to any beaten level. In other words, no additional training. I recorded the difficulty of each playthrough and my opinions on each of their specials. The difficulty scale works as follows:
1- Too easy 2- A bit easy 3- Moderate. Good balance. 4- A bit hard 5- Too difficult
Noob- 3/5 Special can be useful in a good amount of situations. Doesn't cost too much.
Mage- 3/5 Special is effective in any situation, but takes ability to be able to handle.
Warrior- 2/5 Special is often effective. Gets enemies off of you swiftly. Incredibly useful at the arena when surrounded.
Necromancer- 4/5 Special is usuable in any situation, useful in few. They often die before you notice a diffference, especially in the arena. They can be very useful in numbers, though.
Priest- 1/5 Special is useful in any situation and takes little skill to use correctly.
Archer- 3/5 Special is useful in a nice amount of situations. Sometimes not so on bosses, but almost always good to get rid of bothersome baddies.
Rogue- 2/5 To my surprise, his special can be very useful. Attack bosses without them retaliating. Chop down groups who'd normally be all over you.
Barbarian- 2/5 Very fun special, and very often effective. Chop down hordes, and deal good damage to bosses.
Shaman- 4/5 While in most situsations, his special is hardly worth the cost, it DESTROYS arena battles, making it well worth the cost. However, those horde of enemy situations seldom appear in actual stages, making the special usually not worth it.
Paladin- 2/5 Shield can be very useful, especially for stopping enemies who come at you. Also not very costly.
Trapper- 5/5 Special is hard too wield and hardly effective. I like the low cost, though.
The only one I didn't play as was the adventurer, whom I don't quite understand.
Well, none of the bosses, with the exception of the dragon, are very difficult. I did a similar run through with only the necromancer, and never died once (except for a few times at the dragon, but I'm making a point here). But maybe I was just lucky.
Well if you can do that with the Necromancer, I believe you could do that with many other classes.
The point I'm trying to make is that I feel the skeletons don't do too much that I couldn't do without them. However, maybe I just don't know how to use them properly.