Our DM nerfed Polymorph and Wild Shape to such an extent, it could make you cry. So of course Warshaper was nerfed as well. Just because you're immune to "critical hits", doesn't mean you're immune to sneak attacks because you've still got a CON. Figure that one out. Might make your head explode. We do allow the Penetrate ability though, and the DM made it so that the rogue can take it as a bonus feat.
Even though you're immune in your shape changed form, you're not immune in your regular form. I look at this like a Warforged. The poor rogue only has a 25% change of back stabbing one of those things due to them automatically getting Light Fortification at character creation. However, if they take Improved Fortification, they gain 100%. You can take that at like 2nd lvl, so the rogue's out there too.
This is probably the only class and ability the rogue is worthless against. Everything else, you can get crystal (true death, demolition, etc) to do damage against everything else you normally can't crit or sneak attack.
There's always going to be something out there.