What features have 32-bit MCUs in common:

• Registers and internal data paths are 32-bit wide, hence 32-bit microcontrollers
• There is a minimum set of peripherals such as timers and usually an interrupt controller on chip to support an RTOS

Attributes linked to 32-bit MCUs

• Faster and more complex than 8- and 16-bit MCUs but can do a lot more
  Complexity usually comes with peripherals and memory protection. There are simple 32-bit MCUs out there, e.g. LPC2103, STM32F101..
• Harder to get started
  The data sheet / reference manual or whatever the name is, has more pages, more to read more options to do something wrong, so yes somehwat more complex and because of that it might take a little longer to get the hang of it
• Expensive development tools
  GNU implementations exist for almost every 32-bit architecture, so there are free tools available. If a commercial tool is purchased, cost is usually a little higher than for a comparable 8/16-bit tool as there is more need for support, more work for the tool vendor
• Need more power
  This one could be a misconception. More power because it does more but not more power if it does the same thing as an 8-bit micro
• Missing ultra low power standby modes available from most 8-bit architectures
  True because of newest manufacturing technologies used for 32-bit micros, which leads to much higher leakage