When I got my new Droid Bionic, one of the things I was pleased to see was that OtterBox had released a new series of cases for the device upon launch. I've been using Otter cases to protect my tablet devices for some time now, and I am a big fan of their polycarbonate/silicone armor protection.
These cases differ only in that the Defender is a bit thicker with a more rugged design overall, with a full silicone rubber coating around the entire case, as well as being sold with the thick protective holster.
In all honesty, both of these cases will end up adding considerable thickness to your phone, so you might as well go for the Defender if you're a candidate for one of these in the first place.
The Defender has an integrated clear screen protector/cover for preventing scratches and also has the thick holster/cover for stowing the device and for ease of carrying it around -- this is part of the premium price you pay for this case versus the Commuter series.
Like all OtterBox products, all of the relevant Bionic controls such as the power button and the volume rockers are covered with rubber but can be fully manipulated.
The audio jack and the MicroUSB and Micro-HDMI ports are covered with a slicone flap that can be bent back for when they need to be used.
I've only got one major complaint with this particular OtterBox case, and that is that it doesn't support the official Motorola BW8X extended 2760mAH extended battery. It only supports the smaller battery that comes with the phone. And as we all know about 4G LTE phones, they can be very thirsty when it comes to power consumption.
Frankly, I think anyone willing to put an OtterBox Defender on their phone and tolerate extra bulk in exchange for protection is also probably a candidate for the extended battery, so I hope OtterBox releases a version of this case for the larger battery soon.