Posted to Amazon and featured at AVSForum.com, July 2013.

Pros: Airplay, above-average UI
Cons: Stupid rear panel layout

I don't need much in an AVR. I need it to route AV signals from my components to my TV over HDMI. I need it to connect to my home LAN so that I can control it over IP using the Roomie iPhone App. I need it to make good-sounding noise come out of my 7.1 speakers. And I need it to not bug me. By these standards, and considering the blockbuster price I paid for it, I'm thrilled.

There's one thing I need to get out of the way. The speaker connections are of an interesting design: they accommodate bare wire or banana plugs in the same spring-loaded holes. Either way you insert the speaker leads downward while pressing the plastic thingie into the unit. There are two problems with this, one minor and one stupid. The minor problem is that it's slightly less convenient to use banana plugs with this AVR than you're used to: you don't just jam in the plug, you press the spring, insert the plug at an awkward angle, and release the spring. The stupid problem is that if your banana plugs are made of metal, the front right speaker plugs will short against the RCA audio inputs (remember those?) and cause the AVR to shut itself down. Somewhere there is an engineer at Denon who had a good facepalm over this error. Thankfully I didn't brick my E400 after several head-scratching shutdowns, and eventually I figured out the problem, removed two out of fourteen banana plugs and I was good to go.

[Edited to add: I've been told this unit isn't really intended for use with banana plugs. I had thought otherwise, but for the life of me I can't find anything in Denon's materials that indicates support for banana plugs on this model. Just a coincidence, then, that they happen to fit in the way I described. Use bare wire and forget about my banana plug arm-waving.]

Ok. Had to get that off my chest. What else? It doesn't bug me and it sounds great.

I'm assuming a few things about your needs below. If my assumptions below don't describe you, then this isn't the AVR for you.

5 HDMI inputs in the back, one in the front.
Only 4 sets of stereo RCA inputs. It's 2013. You probably need zero of these.
Only two digital audio inputs, one coax and one optical. It's 2013. You probably need zero of these.
Only two composite video inputs (yellow RCA connections). It's 2013. You don't need these either.
Only one component video input. It's 2013. You probably don't need more than one, if any.
Only one HDMI output. Why would you need another?
Only one line-level subwoofer output. One is plenty.
3D supported over HDMI. And 4K. If you can afford a 4K TV now then you aren't buying this AVR. But if this AVR survives long enough for you to take the 4K plunge, you'll theoretically be ready.
Nice UI, both in the setup menus and in the heads-up display. Much nicer and more modern looking than the Onkyo TX-NR616 that died a premature death.
Sounds great. I have a decent set of speakers in my 7.1 system. Mine is not a particularly discerning ear, but if you're a real audiophile you're probably not looking for an AVR at this price point anyway.
It can do "night mode" to compress the dynamic range of incoming signals for use at lower volumes. It has several levels of compression, and it can even apply this compression to TrueHD and DTS-HD signals, which is something my Onkyo couldn't do.
It has Airplay support, which I like.
It can play audio from one source while sending video from another source to the TV. That's another feature I don't think is common.
It can show you exactly what kind of signal it's receiving from its audio source (stereo, 5.1 AAC, DTS-MA 7.1, etc.), and tell you exactly what audio processing algorithms are involved (Dolby PL IIx, DTS Neo6, direct, etc.), and exactly what speakers are active in this mode. I love this because it helps me be sure I've selected the right sound mode for what I'm watching or listening to.

Victory is mine, I love my E400. Great sound, great design (except for that thing about the speaker connections), great firmware. If you have questions about something I haven't covered, ask and I'll try to answer.