ToME: the Tales of Maj'Eyal

You can unlock new classes and races in Exploration mode, so go ahead. As for your problems, it sounds like you might have to learn to scout a bit better or have better ways of escaping. Also, the temporal rift can be very tough for some melee classes. That's just something you have to try and learn.

Spell/Stone is an unlockable tree. You need to kill the random boss Harkor'Zun, who most often appears in Daikara or Tempest Peak, in order to make it available on all future characters.

I tried it on Mac earlier today, and it still broke.