I finally got around to reading A Princess of Mars a few months ago - excellent read by the way- but I had a great deal of trouble envisioning the Martian peoples and fauna. I had to read and reread and rereread the descriptions. I know I could have just googled it and gone on, but I hate to do that.
No offense to Mr. Elmore, but my mental image of Kitiara is way better than his paintings. Kit Harrington is quite a handsome fellow and an excellent actor, but I still prefer the Jon Snow of my imagination. Mental constructs simply have more life and personal investment in them. (The later may be the most pertinent difference.)
Usually, I don't show pictures to players when I'm GMing something. I want them each to build the scene in their minds' eyes. This fuels character immersion, and besides, what they imagine will always be more individually engaging that anything an artist can create. (And waaaayyy better than my doodles.)
|CosmiCat has no Concern|
for Your Petty Human Ways
However, there's a certain break-over point where things are so alien that illustrations are pretty much necessary. (For instance, I google image searched to help me make sense of the Elder Things while reading At the Mountains of Madness.)
It's the mark of an amazing author to perfectly describe the truly strange succinctly. (Honestly, I think Lovecraft put enough in there to visualize the Elder Things, I just didn't have enough in the way of metal energy to puzzle them out at the time.)
When designing your own abominations or aliens or whatever, you can use something more real world or every day as the basis and then pile on the strange. This may help your eventual audience (whether your players or somebody else's) to visualize what you're getting at. Of course that's inherently limiting... so yah.
I suppose it all comes down to this creative balance prevalent in genre fiction* - the opposite pull between innovation and comprehensibility. It's also a matter of supremely personal taste.
In lieu of a conclusion (because I don't really have one), here are some discussion questions:
How weird is too weird, for you and your games?
Do you want lots of illustrations for your gaming stuff or more words?
Have illustrations ever "ruined" something for you?
*RPGs are almost universally emulative of genre fiction