Most of the information for this is found on the Raspberry Pi Foundation Website:
https://www.raspberrypi.org/blog/raspberry-pi-silicon-pico-now-on-sale
 
Now, what is the Raspberry Pi Pico? It is not a another R-Pi computer, but it is a Microcontroller like the Arduino built on a modified ARM-0 (Dual Core) CPU, with a robust I/O. Electronically many of the R-Pi in market can only handle 3.3v at 100ma, thus some sensors being used are muted on their ability to sense, motors and servos operate slowly and relays need to 3.3v compliant and not 5V. Serial Communications need to be put through a TTL Adapter on top of that.
 
The R-Pi Pico being its own microcontroller can operate on the higher 5V environment, while connecting to the R-Pi computers through 3.3v communications without the use of adapters.
 
Spec wise, the R-Pi Pico sits somewhere between the Arduino Uno and the Arduino Mega, based on in-company chip design using a modified ARM CPU. On top of that, R-Pi Clone makers are making their versions of the R-Pi Pico, including Arduino with their Arduino Nano RP2040 Connect. The Clone makers are adding to their R-Pi Pico with various options and built in sensors.
 
The one thing I see in the comments is complaints on how users see the R-Pi Pico will complicate things for the R-Pi Programmers. I can understand that, as it adds another layer of complexity of programming and electronics, but this is also true if you connect an Arduino or another microcontroller to work with the R-Pi computer. The R-Pi Pico simplify things by using the same language subset (Python/MicroPython) for the two boards to work together with.  
 
Being a Mircocontoller, the R-Pi Pico does not have Video or Audio output. There are ways to interface a LCD or OLED Screen to it and program it to display to that screen accordingly.
 
The price makes this quite attractive - $4. The Arduino boards averages at $12, with the Arduino Nano and Micro going for $5+
 
We will have to see what the future holds for the R-Pi Pico.

I never expected this: many on the R-PI: DIY FB groups are giving this Microcontroller bad reviews because their claim is that you can get an Arduino for $2.
 
The $2 Arduino is the Arduino Mini/Pro Mini series, which does not have USB and need a USB/FTDI Serial Adapter to connect to it and program it from there. The Mini is 8MHz and the Pro Mini is 16MMHz. The next is at $4 - $8, the Arduino Micro and Nano which does have built-in USB.
 
The R-Pi Pico has a lot more GPIO pins (30) than the average Arduino (16-20) and a CPU 10X than the Arduino's 16MHz AtMega CPU. There are other things that makes this better than an Arduino on many respects, but Arduino had set the standards and has many support programs and drivers for it.
 
With Price and Function being a major attributes giving the R-Pi Pico a big +. I do not see why they would go against it.
 
Good thing is those who are using it claim that they are great and easy to use.