Figured I'd complete the "set" with the other also-ran 8th gen system, since XBO and Wii U got their threads; do you consider the PS Vita to be a good system, and why/why not?

I've never seen one in person. The hardware seems fantastic. Software? Average at best from my perspective as an observer. As a PSP fan, I didn't even consider getting one. I bought a PSP because the hardware was a marvel for its time, and I only played exclusives and enhanced ports on it. Vita didn't have enough exclusives that appealed to me.

It's the only Sony console that I never experienced.

FUCK YEAH IT WAS! Sony fucked it over with the memory cards and barely any first party support but it got a lot of RPGs. From Falcom like Ys and the best version of persona 4. Some neat shmups. A cool Macross game in Macross Delta Scramble and a good Macross game is rare. Download PS1 games. I liked it more than 3DS tbh even tho 3DS did have SMT and DQ. Gravity Rush was really fun and utilized the system well. A great size and comfy to hold. Snappy UI. Just the stupid memory cards. Sadly the Vita TV which I do have isn't so great as a lot of games don't work on it. PSP and Vita still some of my fave handhelds but Switch 1 took them over as my fave. Vita is love! VITA IS LIFE!

It was (and it is) a good system BUT Sony’s strategy for the console was short-lived; after 2014, the hardware was effectively abandoned due to low interest—driven by the smartphone boom, which was the primary cause. Then there were the memory cards (exorbitantly expensive), and finally, within a year of launch, most developers stopped creating games specifically for the system; for the remainder of its lifespan, releases were mostly uninspired indie titles. A completely wasted opportunity.

It was good hardware, but software was lackluster. Sony gave up on it too soon. So, yes and no.

It's a good system NOW. If it wasn't for the homebrew community and the unnoficial ports, it would suffer from a severe lack of not just games in general, but specially "system sellers". The PS Vita doesn't have a single masterpiece in its catalogue. All of its games, exclusives or not, range from bad to "pretty good". But nothing really stands out except for maybe 1 or 2 old ports/remasters.

Comparing it to the Wii U makes this very clear. It doesn't have a Bayonetta 2. It doesn't have a Breath of the Wild. It doesn't have a Tropical Freeze. The Vita only has a bunch of ZombiUs and Tokyo Mirage Sessions. That's the ceiling of its games.

Edit

Should've ditched the back touchpad and got R2 and L2 buttons. Would've been better for consumers and for devs.

Love the device. Bought it when I was living in Japan, so I have that attachment to it.

Sony went quite hard at first with first party software but games just didn't sell, and so they moved on.

It is. There are some baffling choices like no L2 and R2 and forced Vita memory cards for all models (Vita 2000 and PS TV technically have some memory to use but barely).
It's a sleek device though. Lots of games to play but fortunately not as many exclusives as desired. Remote Play is pretty cool with PS4, I have to say.