In that respect it's much like the official Sonic stories, throwing in more unexplained aliens will somehow fix things the fourth time.
Because the cast is terribly lacking: Besides Eggman, who else is there to cause conflict? The Zeti? IIRC they are supposed to be dead after that game. Dr. Starline from IDW? He's a less competent Eggman. The eldritch abomination of the week? It will be killed/sealed after the game is over, with no carryovers.
Also, Mario's world, despite having even less plot (even then it has at TWO potential big bads at least: Bowser and King Boo), feels more lively than Sonic's world, which currently isn't even sure if humans coexist with the funny animals or not (Youtube videos don't count until a mainline game confirms this issue that has been ignored since Sonic Unleashed). Hell, we don't even have a
name for Sonic's species. Characters are paper-thin and you can't even play dress-up with them (as in, giving them special clothes/gear for whatever reason except for specific circumstances like winter gear) since at some point Team Sonic had the terrible idea to standardize their designs, so everyone looks the same, with all guys having a limited attire and no pants ever, and all of the gals always having a full outfit, with no exceptions.*
The world is supposed to be littered with ancient civilization ruins, alternate dimensions and so on, but it doesn't seem to matter much. Frontiers tried to give character development to the main friend trio (Tails, Amy and Knuckles), but each one is so plain that it falls completely flat. Then there are characters like Shadow or Silver, who are difficult to use.
If the next mainline game is something like Unleashed 2 and explored more of the setting, that would be cool, but I don't trust much in Sega after Frontiers' try-hard plot.
Shadow barely talked and Batman can somehow sense he witnessed a loved one dying after he was rude to them once?
It's the Goddamn Batman (TM).
Tangle the Lemur has a charming character design and seeing how's poorly she's been used in the long run makes me sad.
I don't like her because of how pushed her lesbian romance with Whisper is, even though the two act more like friends than anything else in the comic. It's kinda sad how static the IDW comics are, because the games' cast are frozen and can't have character development due to the stupid mandates, and the OC characters won't matter once IDW goes under.
I liked how Cream the like 6-years old rabbit had to see her mom became a not-zombie robot horror, and she pretty much forgets about it once she's cured, kek. Meanwhile, Whisper barely opens her eyes anymore due to suffering from PSTD after watching her squad die years ago and has remained the same ever since.
*A funny thing I remember is that the protagonist of that VN joke game, the purple civvie, is apparently considered a "they" by the fanbase some reason... Which makes no sense as he lacks pants, which means it must be a male character, confirmed as his official/canon name is Barry IIRC.