From a beginner they are quite a bit more complicated.
When you configure the board in MX all the peripherals have about twice as many options, most of which related to added features which allow those peripherals to only use the minimum amount of power to do what you need and no more.
It's also a lot more picky about it's clocks and clock setup. I think the first time I used it I went straight for 80Mhz. HSE+PLL. It hard faulted on boot. I can't recall what it was actually upset about, I shifted some clock multipliers around, broke the config and hit "Resolve issues" and it came back with an 80Mhz clock that actually worked. Normally the F4s I have don't care and only get picky when you want a 48Mhz USB clock as well. It's amusing watching their clock resolution thing trying to work that one out.
I get the idea with it. You can control so many different features of the chip to reduce power. Instead of the age old external RTC running on a coin cell and a completely inert MCU, you just power the MCU down bit by bit until it's only pulling as much or less than the RTC would.
Further as covered in a scenario in the datasheets and application notes, it is intended to be able to wake on a "low power" interrupt in a low enough power state to run off a capacitor long enough to take care of things before the caps are dead.
That takes care of the issue with "wake on RTC" stuff. Normally the MCU goes straight to full boost more and straight to 100% clock and all peripherals on. The Lxxx can brought down to a very, very low, barely on, 2Mhz mode which draws about 150uA, then put to sleep. Such that when an interrupt wakes it, it barely cracks open one eye, decides it's not important and goes back to sleep without really waking up at all.
I believe they fully intend to run these in 100% battery power devices and have pretty long battery life.
The fact my project is running off USB power with a screen which itself draw 100mA makes probably not the right use case for this MCU. I considered making it 18650 powered and USB charged, which might bring out the features of the L432, but with it being on a dev board for the duration of hte projects life, it's not going to help much.