Liches are rather tough I've found. They generally have a Lightning Bolt spell and a lifedraining spell (can't remember the name, but you can get the same spell in the Wizard page of the skills screen, lower right section)
To kill a lich, what you need are either decent resistances, or a huge health pool plus lots of potions. Otherwise, yes, they're very likely to kill you in one or two hits. (Note, I believe I found 20 Spiritual resistance makes me pretty much immune to the lifedraining spell. Lightning Resistance, I was still taking noticable damage at 30 or so Lightning resist, but it was far less than the amount I took with 0 Lightning resist. Spellshield might help, as it would absorb damage from the Lightning Bolts as long as it's up)
