I think that the fact that the two primary abilities cancel each other out is somewhat irritating. Also, you're still facing the ranger limits on 2 weap, including the double weapons, even if you went fighter to begin with and took ambi and 2 weap as straight feats.
Off hand parry: The higher level you get the worse it is. You're giving up 3-4 attacks for the AC bonus. Yes with a defending weapon and a buckler you can get a big bump from this, but there are better ways to boost your AC without giving up half of your offence.
Also, the 2 weap abilities can be duplicated with standard feats, until the 4 off hands which you get at 20th level. Why bother when you're close to the perfect 2 weap epic feat?
The class is supposed to be the master of 2 weap style, yet the only thing the class gives you that you can't get from feats is it removes the -2 from ambi at 8th level. Weak. At the least they should have allowed full strength damage with the off hand.
The prereqs force you to wait until you're 10th level to take the class. To wait that long, the class should give you more.
Overall, a drab, uninspired and underpowered PrC. For something that proclaims to be the "master" of something, it should let you do something more special than to boost your AC and ignore a -2 penalty which is not that big a deal at 18th level.