I've never bought a system without knowing I'm getting into. So, none yet.

My PS2 back in the day. I got it and then not even 6 months later I hardly ever touched it again. That damn phenomenon known as Halo ate up all my video game time

PSVita. It had been a decade since I got my Gameboy Advance SP and I thought I was ready to give handheld gaming another try. It had a ton of games I thought I'd like, but I'm just not a handheld gamer I guess

Wii and DS. Never enjoyed either of them. To a lesser extent, my PS3. It has some great games but the DS3 is really bad plus the console runs and loads really slowly. TLOU, Uncharted and Resistance keep me from thinking it was a waste of money though.

My Vita and my Xbox One.
Vita because so much opportunity wasted.
Xbox One because I live in Japan and it isn't out here, thus getting games is a pain in the ass, I don't regret owning one, Just wish i had waited till it launched locally rather than it being a once a month DR3 paperweight.

I don't regret buying any. I was however disappointed with the first Xbox. It had Halo which was awesome but that was the best thing about it for me, and I wish I never bought it cause I could have played Halo at a friend's house. 

None. I like all my consoles, gaping flaws and all.

3ds and vita.. Not so much buying them in general really. Just on launch day.. If it is a general regret i would have to say the 360..

The Wii. I only bought it for Xenoblade Chronicles and I haven't played that game in months...or gone past the 10 hour mark.

The wii that shit is a Netflix player now. I had a few games but they bored me. Mario Galaxy was so easy I didnt finish it. What was up with that friend code stuff? I didnt even bother going online