alcaray: Also, I strongly recommend the spell fan of flames, to deal with them. It's tricky to use for 2 reasons (or 3): You have to maneuver the mage around so the fan will hit only bad guys and not your party members, while hitting all of your foes (which often puts your mage where the bad guys can attack him). Also you have to predict where the bad guys will be by the time the spell fires. Once they start teleporting around this can be difficult. Doorways and even corners make great choke points for bunching them up.
If your puller is chased by a roomful rather than one or two, then you can have your entire party keep running. The monsters give up the chase pretty quickly. Sometimes when this happens. you can target the rearmost with an arrow, and pull just that one, while the rest return to their room.
You do have to use smart tactics. And when one thing fails miserably, put it down for a bit and think about another way to try it.
With the Patch 1.03 the things will be a little easier as the mage has an increase on his spells ranges.
I can't speak in the normal setting due I'm playing in the last one (and only resting when my characters are almost death), but the enemies seem to be smart, they focus on the weakest members first (Particularly the shadows). So, you need to engage them with your meele warriors, and in case of teleport do not left alone your mages
. And as Alcaray say it, tactics is everything in this game: Try to make them follow you a small corridors, see if pistols are better option than crossbows and bows, etc.
Engage is similar to attacks of opportunity from the D&D 3.X, however has a big difference: when a creature get inside of the engage range of other will be forced to stop. This is true for your warriors trying to rescue other members, and for the foes trying to reaching your mage
If you begin to explore everything before following the main quest (That is before enter the big city), suddenly the difficult will jump when you reach the second village ( Stupid stone scarabs). And eventually, some random encounters begin to happens that become very hard (Though you can avoid fighting them). At least for me, I had to rest more times in these places (Probably was a place planned for level 7-8 instead of 5) but once I went to the big city everything got "normal" (until I found the next pack of shadows, stupid smart and lethal shadows).
And remember, as you don't get XP by killing, farming is not truly how the game was designed, so, look for secret passages! In this game, if your locksmith can't open the door, probably your PC with high perception will find a key or a secret button, or a high resolve will get info from the other NPC
P.d. IF you has a encounter with shades and shadows, DESTROY THE SHADES First!
P.d.2. I usually don't upgrade weapons until the end, but in this game I was forced to do it, for killing spirits, though giving extra damage to kith is good, so yes, this game is hard.