1. EVERY fucking wolf has a spleen. It's obvious that you're just forcing us to grind shit, don't make the grind more of a chore than it already is.

2. There's got to be about a million more compelling quest objectives than "collect 10 gorilla nipples." If the majority of quests boil down to "[verb] [number] [noun]s" (as most of them do in MMOs, including WoW), then you have succeeded in making a boring quest that reveals to the player that they're just walking on a treadmill.

That type of quest is ok if completing it is incidental and naturally occurs during the completion of actual interesting quests. The Witcher did a great job of this. You could pick up XP for killing x-number of something, but you would usually encounter those creatures during the completion of more interesting story quests.

3. Make combat more interesting that [target] [press butan] [repeat]. Diablo has relatively few quests (most of them boil down to [kill boss]). Nobody minds because the combat though simple, feels good, and is fun for hours on end.

This translates to games of any genre. A lot of modern FPS clearly spent ages on story/scripting at the expense of tuning the combat, and they get boring very quickly when you're not actually in a scripted sequence. The actual gameplay ends up feeling like filler.