1) Use missile weapons! Don't engage enemies at close range unless you absolutely have to, then switch to melee weapons and go after it with your front-liners.
2) Use magic. Chromatic Orb and Magic Missile, even at lower levels, do wonders on things like Carrion Crawlers.
3) If you have a cleric, have him "Turn Undead" while the others are fighting. That way, you won't get swamped by skeletons upon entering the crypts.
4) Strategy: What you are doing is working your way through the Vale to the crypt at the top right of the map (that's Kresselack's Tomb, and you need things from some of the other crypts in the map before you tackle it.) That should be the last crypt you face.
5) The middle crypt (where all the chests are and the tents) you will come back to after Kresselack's Tomb. Meanwhile, loot the goodies that are in there first, as they will be a great help in taking on Kresselack's tomb.
Hope this helps.
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