I don't mind what the style is, for me it's all about clarity.
Whether it's line art or lineless, colour, black and white or greyscale doesn't matter. The thing I'm looking for is how the artist uses their lines, shading, colour or tone to clearly get across things like the relation between characters and objects and the space they're in.
Can I tell who is who? Can I tell where they are in relation to each other? Do the poses and expressions read clearly so I can tell what they're feeling and doing?
Usually in comics this means the lineart is doing the heavy lifting, but in some softer or more painted styles, this falls more on the shading or tone. What I'm looking for is art that shows the artist is adept at getting across depth and volume in their chosen style.