Whenever I log into a MMOG for the first time, my immediate action is to go to my graphics and start setting everything up.  Some games have a system detection that will (hopefully) give you the best set up for your machine.  Unfortunately I used this feature in Aion and it didn't do what I had hoped and I do not recommend using it.  It changed my settings much lower than I would typically run and changed my resolution to something that I would consider unplayable. Texture detail and shader quality just make everything look prettier, but the difference you will see between moderate settings and high settings is minimal.  Put these towards the middle of the slider and you'll be rewarded with a bit more speed in performance.

Shadows are nice to see, but they take time to render on a mediocre machine so they aren't really worth having.  Turn them to the lowest setting!  This will relieve stress on your video card and will make things run smoother. Water effects in Aion look awful on the lowest setting, but this also takes time to render so rather than turning this off, set it to a moderate level using the second or third bar.  I have mine right in the middle of the scale and it makes water attractive without making it use up my resources. Background, terrain range, and object range are things I like to see.  If you are playing in game, it's helpful to see what's coming at you before it smacks you upside the head.  Most system should be able to handle having these at a moderate to high setting without taking too big of a hit to performance.  I feel that what you gain in visibility is worth what you may lose in render speed.