Zileas: If the races aren't different on some level, there's no point in having extra races. If they are only slightly different, it's a feature that might be taking away more than it adds, which is why we are trying very hard to make them as different as possible.
We make them different in several ways. First, the most obvious, is that they feel different - each race has a different story behind it, a different society, a different approach to the world.
The second is in the way the units work. We try very hard to make all the units, especially intermediate and advanced units, completely different from the other races. Sometimes this is only a subtle difference, but sometimes there's no comparable unit. In the case of basic units, it's hard to avoid some similarity, but then again, no RTS has ever gotten around that difference very well.
The third way is in the strategy which sets the race has as a result of the units. Each race favours a different overall set of strategies. For instance, the dark elves are very much about keeping your wits about you and getting the jump on the enemy, since they have a number of spells that in combination are devastating at close and medium range.
The Accursed on the other hand favour a more deliberate, slow, cautious approach, due to a few of their units being useful for "pushes" and things of that nature. Their mobile production also makes a lot of interesting approaches possible.
The third race, which we haven't announced, is highly mobile and recon-heavy. Their units don't perform as well at high levels on their own, but their superior mobility and such can be used to your advantage to bridge the gap. Our unique resource system makes the third race work in large part. I'll give you two examples of things we're testing right now with this race that will probably stay in. The first is a unit that can set an "anchor point" and has a ”teleport" ability. Basically, you can attack something with it, but if the going gets tough, you can teleport away. Naturally, you can't use this ability too much, but that's an example of superior mobility in an otherwise inferior unit. The new race can also open a 2-way portal between two points with one of their ritual spells, among other things.
All of them involve totally different strategy sets, which means that each race has a unique match up against other races.