"Good" page layout serves two functions:
1. It makes the contents of the page easy to read.
2. It's pleasing to look at.
Ease of reading ought to be of primary importance, IMHO. I've seen pages running the gamut between easy-to-read but boring to look at and "artful" but nearly impossible to read... I prefer being able to read!
As a caveat, I'd argue *both* of the items I listed above are qualitative and idiosyncratic judgments. What *I* find easy to read, other people will find distracting and frustrating, and vice versa. What *I* find pleasing to look at, other people will find garish, boring, or something else... and vice versa. There is no "golden design" just as there is no "golden ruleset"; you can't please everyone every time, after all, even though you might be able to shake out something of a consensus if you work at it.
I happen to agree with Erik that the 3E core books' page layout is a vast improvement over past layouts (as I've already said), but my further opinion is that the primary improvement has been in "look." As an experiment, I think the 3E core books were a fantastic success: I like the margin art, I love the fonts (I wish I owned that Celestia Antiqua, lemme tell ya

), and I find the pages clear (apart, as I said, from the brown "wet notebook" lines). I'm also a big fan of the layout featured in the new FR line.
Stat blocks crossing pages can be fixed (see Fiend Folio). Brown lines can be fixed (see all core books published after the first 3). White space around art can be fixed. Overall, I think we have some smashingly attractive, easily read books and to me the difference parallels that between fine cuisine and fast food (laying aside considerations of price and preparation time). Sure, fast food is serviceable and fills the empty spot, and it's even likable sometimes; but if you have the opportunity....
Just so it's clear where I'm coming from, my favorite 2E layouts, in order from "excellent" to "good," are: Planescape, Birthright, Mystara, the 3 FR deities books, and Monstrous Arcana. The rest strike me as varying from "a bit on the lame/boring side" to "ugly." Easy to read, sure (and I've reservations on this point concerning the "black books"), but still.
Personally, I think a judgment regarding page layout should be separated from a judgment regarding art quality. Picture your favorite artist (or pick from your short list) and your least favorite artist (or pick from your long list

) in that spot instead of the art that is actually there: to the extent that it doesn't make a difference, I'd say you are evaluating the page's layout.
Just to keep it unclear where I'm coming from, my favorite 2E art appeared all over the place. I won't name any names; I don't think a "favorite artist" discussion is on-topic in this thread.
You see, as a desktop publisher myself, page layout is one issue I sort of take to heart... what is "good" and "attractive" layout is of professional interest to me. I can't really say I make purchasing decisions based on it, because I've been buying the Arthaus Ravenloft stuff; I do like it for its content, but I find it kind of "bleh" layout-wise. (I don't even like the fonts.

)