Here is a bad design decision that seems easy to band-aid. Guild Wars starts missions in Prophecies and Nightfall with a button under the character list, while in Nightfall and Eye of the North with an NPC dialogue. This is poor, having something be a UI element in one place and part of the world in another. I started in Nightfall, as most seemed to recommend, then played some Eye of the North and just this week visited Factions. Nothing tells you about the “enter mission” button. There is absolutely nothing in-game that tells you how to start the mission unless you notice that a button appeared in the UI.
I have commented on how Guild Wars players and wikipedians assume that you have a sizable resource base. It reaches a new tier when the developers forget that they designed the game as three expand-alones rather than a base Guild Wars with expansion packs (and then one actual expansion pack shared across the three). There is a handy mission to introduce you to the other campaigns, but whoever wrote it must never have thought that you might be starting with Nightfall and not already know how things work in Prophecies and Factions.
The in-game help is already a link to the wiki. Your players should not need to then Google to try to figure out what they need to ask the wiki.
Psychonauts did the same thing by giving you inventory items without telling you that you have an inventory or how to access it.