"Photon soup" as I like to call it, is the phenomenon that arises in games from many flashy effects going off at once, decreasing fight readability and turning things into a mess of hopeful guesswork. This is a problem that most mmos have, with guildwars combination of fast paced action combat and array of aoe skills making it one of the top offenders in this regard. There is no real cure for this other than tearing it all down and starting again, so what can we do to help?
There are a couple of ways to mitigate photon soup, if not cure it completely. The first of this I'd like to see is the priority of damage numbers. getting a critical hit in this game causes a big red splash to obscure your target for a couple of seconds - vital seconds that the enemy are probably using to cast a skill - one you can't see and react to, because of the damage numbers. I want to see numbers be rendered behind the target, or reduced in size, or toned down in some way.
Another way would be to tone up the outline of targeted enemies, or even all enemies. If you've ever played an rts and had your units move behind something, chances are you've seen a coloured silhouette showing you where they are so you can still read the situation clearly. This actually already exists in guild wars to some degree, in the form of a red outline around your target that will render through effects. My problem is that this outline is too small and is still obscured behind damage numbers, making it not nearly as effective as it should be.