Overall DKS is a little easier, but a harder difficulty level was added to compensate.
In D2:ED there was a strong character level effect to combat, so opponents more than a few levels above you were impossible, and more than a few below could not hurt you (making for boring combat). In DKS the effect was reduced, so that higher level opponents were tough but not invulnerable, and groups of weak opponents could still be a bit of a threat.
There were some changes made to quest experience in DKS to make levelling a little easier at the start of the game (to address the difficulty spike when getting access to the full Broken Valley) and opponents at the start of the fjords were changed and the experience increased to help with the difficulty increase then (though not nearly as many people had trouble there), etc.
In D2:ED, for example, I got access to the full Broken Valley on level 6 (after doing everything I could), and a couple of the opponents in the dragon sequence brought me up to level 7; In DKS I got to level 7 just after the dragon sequence, but with lots of quests left to turn in.
There were additional sets and lots of unique equipment added in DKS, which can make the game a little easier. Playing a ranger, once I got the first unique bow available I never saw random loot that came close to being a replacement. Some of the ranger skills were made less effective, though (not sure how overpowered they were in D2:ED, since I played a warrior).
