I'd say that I'm a bit surprised that this receiver wasn't more popular, but I can understand why it isn't. I fills the very specific need of "Denon AVR1912, but shorter". I say "Denon 1912" because that is essentially what it is. Anybody coming along later wondering what people think of this receiver, just go look at the enormous Denon AVR1912 thread. Any joys and annoyances that you will find there will hold true here for the Marantz NR1602. They are both made by the same company, contain the same software, and are extremely feature similar. The only real variances are the output power of 50W/channel versus 90W/channel, and 4-port HDMI switching instead of 6-port. This receiver exists for the people that want to fit the 1912 feature set in to a <6" space.
Doing a quick search for "NR1602" in this forum shows a concern that the receiver is only 50W. One post even claims that it will only reliably spit out 23W on the test bench. Let's assume this is true, and let's also assume that the AVR1912 spits out a perfect 90W all the time. What does this actually mean in the real world? Normally nothing, as most listening, especially when paired up with a powered sub, never exceeds a couple of watts. According to entry-level audio theory, it takes twice the power to cause a 3db increase in volume. This puts the difference between 23W and 90W at roughly 6db.
Let's do some quick back-of-the-napkin math!
Using perfectly average 89db/W efficiency speakers at say 8 feet, that puts you at roughly 4W required to reach reference levels of 85db. 85db is of course freaking loud, and the vast majority of us don't use much more than 75db in our homes, with a power requirement closer to 0.5W. Going the other direction, 90W lets you reach roughly 99db with this fictional setup, while the NR1602's 23W still gives you a "GODDAMN THAT'S LOUD!" 93db.
In short: 23W versus 90W means very little, and 50W versus 90W means even less. The power rating is not a reason to skip over this receiver.
So, I've had mine for about a month now. Audyssey MultiEQ is fantastic. AirPlay is close to magic. The build quality is not nearly as good as the Yamaha RX-V2500 that it replaced, but it's also a $650 MSRP receiver versus $1100 MSRP. I wish it had dropped most of the analog inputs in favor of the two extra HDMI inputs that the AVR1912 has. The thing looks great, and more importantly actually fits in my new stand. The UI is convoluted and is poorly documented, as all Denons that I have ever touched are.
If I had the space, I would have picked up an AVR1912 and not a model higher, nor lower. $100 less and two more HDMI in. The loss of network features on the AVR1712 would suck, and the network plus drop to 5.1 would suck on the NR1402. In general, the NR1602 is a great little receiver that serves it's function of "short 1912" very well. Once one gets through the poorly documented setup, it functions fantastically in day to day use. MultiEQ sounds great, and it does everything else that you would expect a modern receiver to do.