I have a few questions before I make the purchase.
Question 1: I have heard some issues with the speed of the game on modern systems. Is there a sure way to correct this?
Question 2: are there any other issues on modern systems?
Question 3: Dwarf or Barbarian?

1. I've had no issues with speed, but it did take a trick to get the game to run and not look like utter garbage. There's some help to be found in the forums here if you do run into those issues, however.

2. See answer one. The problems involve which graphics driver to use.

3. Man, the Barbarian is fun, but I find to be the hardest class...which sort of makes it the most rewarding. I'd go Dwarf first. Really though, play all the classes. It's an entirely different game/story with each one.

I read a little more about the dwarf, and he is slow, so I settled for the knight.

Knight is generally most recommended, devs supposedly spent most time on him. He is the only one with ability to wear 3 armor types and has plenty of combos.

I found him to be easier than the knight for some reason. The enemies in the game, especially early on can't take more than one hit from my chaos sword (starting weapon).

After acquiring the long sword the game becomes less frustrating.

The babarian I found to be VERY weapon specific, put non-two handed weapon on him and he swings it with his whole body like a stumbling ogre.

*Tip, the scythe is good on its own, the special is a pile of Sadams rhetoric about freedom.

Start with Dwarf. The barbarian is nice, but difficult to learn. Ideal for your second playthrough. Do not miss this game. Plus, you may even like it so much, as to finish it with all four players, and more than once.