Morbane has the right of it: you have to do quests the way YOU like to do them.
Building a mod/campaign/game like this is just as creative of a process as making art or writing music. Imagine if your favorite kind of music was hard rock, and then you decided you were going to make your own music. You decided that instead of doing what you really enjoyed, you were going to do what was popular, or what you perceived to be popular, so you decided to write music in the vein of "p!ink" or "Phillip Phillips". That's a far cry from hard rock. People can hear a lack of passion just as much as they hear passion in work you enjoy doing.
So... you gotta do what you enjoy.
I always go back to something I read in a book that I'm a big fan of (more on that later), and the advice is: story is king. It is the single-most important aspect of what you're doing. How do quests further your story? How do they make it better?
Sure, we're building video games here, and quests are a part of it, but I feel they do their job the best when there's some context within the story you're trying to tell.
Kill X monsters is a famous, oft-used quest design, but how can you blend that with the story you're trying to tell, and make it slightly less obvious that you're really sending the player to kill X monsters?
Make it about the story.
As an example from my mod: One of the first quests you do in my mod is go kill 10 rats. Only the character you get the quest from never says, "go kill 10 rats and bring me back their teeth/hides/claws". No. Instead, the quest-giver mentions how the warehouses that store the town's grain and supplies frequently need to be purged of rats. It's a common job that he often hands out to youths. The quest giver doesn't tell you how many rats to kill; just to clear the warehouses out and report back to him.
It's a super-easy quest to setup, but it fits with the lore of the town and the larger story being told. It's a simple quest that gives the player a chance to acquire a meager weapon (before they go slay the rats) and gives them the opportunity to kill a few simple creatures. Nothing complicated, but again - fits in the story.
It's a subtle difference, and any experienced game player immediately recognizes it as a "go kill X creatures quest", but it has some context. It just "feels better", IMO.
Figure out what kind of story you want to tell, and build quests based on that. Side quests are a time to get away from the main story and do some more interesting things, like puzzles and such.
But most of all, go back and think about the quests you enjoyed the most in games you have played. Figure out what it was about those quests that you really enjoyed, and then go build some quests similar to that.