Its interesting that criticism is focussed on price. To me, the Due price (in Europe, which includes 20% sales tax) is fair. I think the strongest competetion is from boards that offer more capability (but are also more expensive).
For example Cubieboard, at US$49, has much higher computation capability and decent graphics (yes, its not a real time board, and it has an OS):
1G ARM cortex-A8 processor, NEON, VFPv3, 256KB L2 cache
Mali400, OpenGL ES GPU
512M/1GB DDR3 @480MHz
HDMI 1080p Output
10/100M Ethernet
4Gb Nand Flash
2 USB Host, 1 micro SD slot, 1 SATA, 1 ir
96 extend pin including I2C, SPI, RGB/LVDS, CSI/TS, FM-IN, ADC, CVBS, VGA, SPDIF-OUT, R-TP..
Running Android, Ubuntu and other Linux distributions
or looking more at embedded solutions, the ArduCopter community (which started with a Mega2560 clone and then moved upwards in compute power and integrated sensors) seem to see the main benefit to them of the Due launch in terms of the multi-architecture 1.5 IDE. The actual Due hardware is cheaper but less capable than what they are focussed on, such as the VBrain (highe compute power with floating point unit, integrated sensors) at EUR 199:
168Mhz ARM CortexM4F microcontroller with DSP and floating-point hardware acceleration.
1024KiB of flash memory, 192KiB of RAM.
MEMS accelerometer and gyro, magnetometer and barometric pressure sensor.
8 RC Input standard PPM , PPMSUM , SBUS
8 RC Output at 490 hz
1 integrated high speed data flash for logging data
1 Can bus 2 i2c Bus
3 Serial port available one for GPS 1 for serial option 1 for serial telemetry.
3 digital switch (ULN2003).
Jtag support for onboard realtime debugger.
1 Buzzer output.
1 Input for control lipo voltage
or the DIY Drones PX4 (higher compute capability, FPU, integrated sensors incl. GPS) at USD 149:
- ARM Cortex-M4F microcontroller running at 168MHz with DSP and floating-point hardware acceleration.
- 1024KiB of flash memory, 192KiB of RAM.
- MEMS accelerometer and gyro, magnetometer and barometric pressure sensor.
- Flexible expansion bus and onboard power options.
For the small, light and inexpensive ARM project the Teensy 3.0 looks great. For the larger, more compute intensive (e.g. audio processing) projects, I wish there was something more like these Arducopter/UAV boards, retaining the good compute capability especially the FPU, but dropping the airborne-oriented sensor package. I would have thought that not including GPS, magnetometer, 3-d accelerometer, gyro and barometric pressure sensors would drop 50 to 75 USD off the base package. Soething like that in Mega/Due style board layout would be very attractive (and yes, it would be around 80 to 100 USD).