For the most part I like the designs. I prefer the one with the organ pipe cactus the most:

They should have posted these images in PNG format rather than JPEG. The flat colors would have rendered better.
The type design is really good. The typefaces chosen aren't run of the mill fonts bundled in with Microsoft Office. The overall design will be pretty legible, provided the sign panel sizes are appropriate to the highways where they're installed.
The only criticism I have about the designs is the scenery in some of the designs looks like is was
auto-traced or maybe painted with the "blob brush" in Adobe Illustrator. Some of the objects look kind of blob-u-lar and ill-defined. If the vector-based objects had been digitized by hand over the top of photographic imagery or a sketch the various objects would have looked more precise. But doing that would take more time (but not all that much really). Overall it's a judgment call in how far one wants to go in refining a sign design. Maybe ADOT's thought process was vehicles would be speeding by these things at 55mph-70mph. The scenery doesn't need to be so sharp and precise. My own feeling, as a very experienced sign designer, is people do more than just whiz by these kinds of signs. More than a few people on long road trips stop, get out and take pictures of these border landmarks. They'll take a selfie in front of a sign like that and post it to Instagram. In those respects the sign needs to look better for close up uses. The background scenery doesn't need to look like it was churned out of Adobe Illustrator's Live Trace filter.