I love the idea of side quests, but I have a problem with all the player side quests that we have: they don't do anything until you finish them. The quests we got in the Angmar Awakened cycle all have triggers upon completion, and so far all the spoiled side quests we've seen for the upcoming Haradrim cycle have to be in the victory display.
The reason I don't like them and never play them is because most of the time, if I am completing quest stages, it means I must have the game somewhat under my control. So while the effect can be quite powerful, it isn't really needed in order for me to win. I'd rather fill my deck with cards like feint, that help be prevent a character from being destroyed, or spirit Bofur, who can help me quest successfully when I would have failed.
There is no reason why side quests can't have instant positive effects when you play them. But they must be properly balanced, because if they have a positive passive effects then people will just put them in play and never explore them.
Here's an example of a side quest I'd play:

This side quest provides an effect that helps me when I'm behind the instant it enters play. It also offers me an incentive to choose it as the active quest. You may think it's overpowered or underpowered, but regardless, this type of player side quest is certainly possible, and I have more ideas for positive-passive side quests for the other spheres.
The are other possibilities too. You could have a side quest that has a positive-passive effect, but when a character is destroyed the enemy makes progress on it, and if it gets completed something terrible happens. Or you could have a side quest that grants an immediate bonus but then has a negative effects until it's explored, like this:

This provides a really great benefit that scales with the number of players, but it carries a heavy risk. These are the kinds of cards I'd love to see more of.



