I feel like it's really polarizing, actually. I've met a lot of people who liked it and a lot of people who disliked it. I just didn't feel that "connection" to the game or the world or the characters that I did with the first two games. The first two are easily two of my favorite games of all time, so maybe my expectations were just too high.

Granted, I have yet to play the first two you mentioned, but looking at them they definitely have a different feeling to them. To me, SPM kinda looks almost like more of a spin off but maybe I'm off. I never really felt that connected to the characters either, but there were a few I really liked and some of the levels were really interesting like the one with the chameleon. But I'll definitelty have to play the others sometime in the future. 

Smashing Drive, god damn I couldn't even beat the first race I gave up playing then years later tried again still couldn't. That was the first game I regret buying.

Kinda surprised so many people mentioning current gen games as their first regret though.

Its easy to hate new things.

The first game that I regretted buying is difficult to determine, due to receiving games from other people and not enjoying some of them. I have to remember the first game of which I bought and that I disliked.

1st retail game that I bought and disappointed me was Pure.
1st Indie game I bought that I was disappointed with was Toki Tori 2.

Resident Evil 6, for PS3. I never expected the Leon campaign to be a survival horror like many delusional fans, but I also didn't expected it to be Karate Kid meets zombies. I mean, wtf was that? Soooooooo action oriented and chaotic that I killed most zombies with kicks and punchs. Jesus!

And that comes from someone who liked even RE5.

This question seems more towards the newer generation of gamers. Unless you're asking me to take a wild guess on games I've owned for 20+, then I couldn't tell you. Lot's of crap on the older consoles I regret purchasing. Lot's of crap on the newr consoles as well.

Most recent game I regret purchasing is The Walking Dead Season 2 on the Vita. The first one had near unplayable framerates. Why did I expect any different from the second? Oh yeah, it was $5 that's why. But yeah. Quit at the first chapter because the QTE framerate when doing something is trial and error. Whether you do everything perfect or not, the framerate is so bad it doesn't recognize it so you're forced to memorize the entire section and repeatedly tap the correct direction. After finishing that part didn't care to play through anymore of the game.

Ff13. :(

Although its not the first one the one I still regret buying the most is SaGa Frontier its just not very good couldn't force myself to actually beat the game huge letdown by Square after FF VII and FF Tactics.

Spyro: Enter the Dragonfly, the game that pretty much killed my love for the dragon. While Crash Bandicoot: Wrath of Cortex functions (Besides long load times) and can be as fun as the first three games, Enter the Dragonfly is horribly buggy, severely repetitive, and it's just not fun for me.