The problem is that it has NOTHING that cannot be done BETTER by two other classes.
The Shifter has the following: Full BAB, 4+ skills, d10 Hit Dice, animal aspects (3+level in minutes per day), wildshape, claws.
the Feral Hunter archetype for the ranger has all of this, save for the class, full BAB, and d10 HD. It makes up for these faults by having weapon proficiencies that the shifter lacks, spell buffs to make up for the BAB and Hd loss, and animal aspects that last permanently rather than a limited duration per day. It is equivalent in power as far as wildshaping goes. Hunters also have 6+ skill points, and a greater range of skills to use.
Druid has the same BAB and HD as Feral Hunter,, superior spellcasting, and wildshape only a single level later. In exchange, it gets a slew of ribbon abilities, and even better spellcasting than Feral Hunter, going all the way up to 9th level. this isn't even getting into the fact that being a druid gives you an animal companion, which if used correctly can add a near PC-equivalent melee combatant onto the field, making you one and a half characters outright.
As far as the claws go? they have a far, far shittier unarmed strike mechanic than even the monk has (as Monk has Flurry of Blows and full BAB if you're playing unchained), lack iteratives, and don't have even the damage of monk unarmed strikes, making them inferior in every way. Monk also has a an equivalent "wisdom to AC" mechanic, making it superfluous on the Shifter.
The reason the Shifter is bad isn't that it does nothing. It's the fact that it does absolutely nothing that other classes don't do better and lacks the supplementary mechanics that make those initial mechanics work. It is, in fact, worse than vanilla rogue.