After finishing Sacred, I was happy to see that I could take the same character into Underworld so dove right in. One thing I've noticed at least in the first few quests is that I can't take more than a few steps without having to fight a bunch of somethings. Going from Point A to Point B to begin the quest is bad enough but then it's fight the same bunch on the way back to tell whoever told me to go on the quest that it's done. It reminds me of trying to play Final Fantasy 1 on my PSP where the same thing would happen -- same old fight over and over just getting from somewhere to somewhere else. Combine that with the fact that it seems to take much longer to get from one point to another in Underworld and it just comes across as less fun and more of a chore.

I just recently finished my first Underworld campaign and would have to agree with you. The respawn rate is high even on Bronze level, the portals are somewhat tedious to find compared to the Ancaria Campaign (looking at you, Dwarven Ruins), and most of the new areas just seem to be deliberately twisty to maximize the amount of distance you have to travel to cover relatively small terrain.
Maybe I'm just spoiled by the largely open areas of Ancaria, with portals very close to most of the cities