As for Sonic, I'll stick to the usual "Adventure 2 was golden" footnote. There was some great dialogue in that game.
PPPPPPPPPPPPPPFFFFFFFFFFFFFFFFFFFFTTTTTTTTHAHAHAHAHAHAHAHAHAHAHAHAHAAAAA
In relation to other INCREDIBLY corny and seriously derangedly retarded dialogue that other games usually seem to have... yes, it was decent. But it had few examples. While the rest was completely forced and really bad. Overexposition for kids, no interesting exchanges except for the Shadow/Rouge dialogue, and while some characters show little about what's happening while relying on simple events to follow it, others go "AMY IS WITH EGGMAN. I MUST RESCUE AMY. BECAUSE SHE IS IN DANGER. BECAUSE EGGMAN IS EVIL. GET IT KIDS?" Pretty much everyone behaves as if they were meeting for the first time, the awkward pauses and the crazy [parasitic bomb] that happens in certain parts of the dialogue is unforgivable.
But yes, it IS standard for videogame dialogue to be cringeworthy most of the time. The way I'm comparing it to MLP, is because MLP characters actually act like normal individuals. While Sonic, Mario and many other characters act like they're reading from a damn script, trying to act out a very badly-paid play written by high schooler fan fiction artists.
Let's compare some stuff:
[youtube]http://www.youtube.com/watch?v=P4V5pKF7gyM&feature=related[/youtube]
Repetitious exposition, characters seeming like they want to show every single detail several times so that kiddies won't miss it, and don't leave any kind of logic to the people watching it. They address the audience, not each other. They are telling a story instead of talking.
[youtube]http://www.youtube.com/watch?v=qD97UvLnluk&feature=related[/youtube]
See, here, you got JUST enough exposition without seeming like they're talking to the audience, plus, it's incorporated INTO the dialogue. They speak to the characters, and tell them what they need to know, while revealing their personalities and quirks and not devolving into simply exposition mouths.
[youtube]http://www.youtube.com/watch?v=TwJ3gghVtVs[/youtube]
In comparison, this scene would be "WHY ARE YOU ACTING CRAZY AND NONSENSICAL WHEN YOU SEE THAT I AM SUFFERING IMMEDIATE DANGER FROM THIS FLOCK OF CREATURES PINKIE PIE? I AM RARITY AND I AM IN DANGER"