from experience, multipath is hit-or-miss with ALL the GPS apps (i've used Wayfinder, TomTom, and Nav4All heavily) Most will try to get you to make a u-turn for quite a while, before finally realizing that you didn't want to go that way (or couldn't)
As for tunnels and whatnot, living in Dallas, TX, that's going to be incredibly hard, if not impossible, to test. But they generally remember where you last were.
Thus far, I've decided to focus on installation, presentation (menus look/feel/usability), speed and ease of creating a trip, "favorites" and ease of those, accuracy, and POI. Anything else?