The spell lists everything you gain from the effect:
While projecting your shadow, you gain a shadow’s darkvision, defensive abilities, fly speed, racial stealth modifier, and strength damage attack. You do not gain the creature’s create spawn ability, nor its skill ranks or Hit Dice.
On defensive abilities, you gain incorporeal (immunity to non-magical attacks and no strenght score), undead imunities (too many to list here) and channel resistance (makes you harder to be turned by a cleric). You can see in the dark for 60 feet, you gain a fly speed of 40 ft. (good), and +4 Stealth in dim light (–4 in bright light)
Finally, the strongest ability you gain is the Shadow Damage attack. Normally, a living creature does not die from Strength ability damage, but the damage caused by shadows can kill.
A shadow’s touch deals 1d6 points of Strength damage to a living creature. This is a negative energy effect. A creature dies if this Strength damage equals or exceeds its actual Strength score.
Everything else is calculated based on the caster's stats, his dexterity doesn't change, his base attack bonus doesn't change, and his hit points doesn't change.
PS: That spell is insanely strong. It lasts hours per level, and if you face no magical resistance, you can lay down death upon a small military camp or village.