Right of the bat I must thank flakko for an AWESOME deal on a great amp.

This review is being written by a relative noob(me) to car audio who may not be up to speed on the technical terms but knows what he likes and more importantly what he doesn't.

The IS series may be an entry level model of the USAmps line up but looking at it there is no compromise when it comes to quality.
It has all the functions that you may need or want for the front and rear channels(LP,HP,etc....), to obtain a good sounding system and it's easy to configure to a variety of uses. These controls are clearly marked which turned out to be a bonus in a low light situation and easy to get to at any time.
All RCA connections(front, rear and line out) are on the same side of the amp as all the adjustment controls with the speaker and power wires on the opposite which makes for a clean install.
With a slight amount of trimming I was able to connect my 4AWG power wires into the terminals which are spaced a good distance apart and sealed in plastic (no accidental short circuits with a dropped screw driver here).
Both ends of the amp have covers that follow the lines of the amps body and nicely conceal all the wires. They come off with just 2 screws each and in my case will be used to make the install nicer (once all the trim items are done I will post a picture).

Now to the good stuff,
I have this amp running my CDT components up front with a pair of 6x9's in the rear and the sound is simply amazing. Clear, loud without any signs of noise or distortion except for some rattles from my cars interior pieces.
Friends with systems in their cars have complimented on the clarity of my system and when the need arises (which is all the time) this amp pushes quite a bit of volume out of my speakers.
I have run the amp hard for several hours and it took it like a champ staying nice and cool the whole time.

As I'm sure you can see by now I am more than happy with the USAmp IS-4085 and recommend it highly to anyone looking for a 4 channel amp along with the rest of the USAmp line up..
When a manufacturer puts so much effort into the way their product presents it self than just think about the effort that went into making it preform, looks great and works great.

To sum up my rant, the only draw back of installing this amp is that now I need a stronger amp to power my subs as the current one just ain't cutting it.