Here was the breakdown for the 10th level character (Druid 7, Nature's Warrior 3). Note that whenever Nature's Warrior said "Wild Shape" we substituted the PHBII variant ability:
S 18, D 12, C 18, I 8, W 14, Ch 8; Saves: Fort +12, Ref +4, Will +8; HP 116; BAB +8; Feats: Tracking, Toughness (Variant that skips the +3 hit points and skips straight to +1 hit point per level), Power Attack, Cleave
The Nature's Warrior abilities taken boosted DR to 3/- and AC by +3.
That left us with the following while in Slayer (the most commonly used for combat) form:
Attack routine: +17 (Bite), d8+10, +12 (Claw), d6+6, +12 (Claw) d6+6; Speed 40'; AC 21 (touch 11, flat 20); DR 3/-, Improved Critical. Now this isn't really all that bad - about par with a fighter of the same level. Things look to get worse, however, as the PC progresses, and we add levels of Warshaper on top if it (immune to crits? Reach with natural weapons?). In addition, we couldn't figure out how to apply spells to the situation - does barkskin function throughout the forms, or end when a new form is taken?
We then took a look at the spells the druid could bring to bear (spike stones, entangle) and decided that while the druid looks different on paper, it hadn't lost any of its former power.