I played a druid with this feat back in '04 or thereabouts. I found the Silver Dragon to be a good utility form. Immunity to both cold and acid. Throw on an Energy Immunity (fire) spell, and you were immune to three types of energy damage.
Its alternate form ability also effectively gave me four wildshape forms for the price of one daily use.
Alternate Form (Su)
A silver dragon can assume any animal or humanoid form of Medium size or smaller as a standard action three times per day. The dragon can remain in its animal or humanoid form until it chooses to assume a new one or return to its natural form.
It could be argued that using wildshape (a Supernatural ability) is a purely mental action. If you are already paralyzed, use your mental action to wildshape into a dragon and become unparalyzed.
Really the advantage is that the Dragon Wildshape feat is a big tool box of utility.
Fighting something with crazy-high Spell Resistance? All those (Su) abilities are not subject to spell resistance.
Fighting a cold subtype creature? You have unlimited fire attacks, and vice versa.
Just got subjected to a disease? Become a styx dragon; now you are immune.
Turn into a Rust dragon and destroy all the enemy mooks' weapons, and get rid of the BBEG's armor.
You are fighting incorporeal creatures, and your druid has no Force effects. Turn into a radiant dragon or an amethyst dragon and deal with the thing.
Chaos dragons have immunity to compulsion. That's handy when infiltrating the Mind Flayer hive, etc.
I will grant you that the shadow dragon IS the best form, but there are other good utility abilities available through the feat.
Deep Dragons are another good form. Up to +14 natural armor, and a DC 19 breath weapon that deals 8d8 damage (of a type that has no resistance). And always-on True Seeing. And immunity to charm effects. And resistance 10 to fire and cold.
Song Dragons can get up to +16 NA, a DC 21 breath weapon for 10d6 electricity damage, also have True Seeing and Tongues, and are immune to electricity and poison (though a druid would be immune to poison by this point anyway).