The gameplay, voice acting and story. It's simply a common trend to hate sonic games these days because of their poor reviews. Heck I bet most reviewers didn't even play the game and just gave it a poor score because it's the common trend with sonic games.
I had as much enjoyment with Boom as I did 3D world.
What.
Story and Sonic Game. Good. Pick One. As Alex Day puts it, Sonic doesn't need a story.
And contrary to your belief that "The reviewers just gave it a poor score" the Last 3 Sonic games all have above a 60%, with Generations and Colours getting an 80% on Metacritic. That's not a BAD review, that's just a flawed but still good game. Compare that to Boom, which has a 40% as an average. No, it is not Sonic hate, it's just the game sucks.
The gameplay completely misses the point of Sonic and when it does get sonic(Go fast), the framerate completely screws it up. There are numerous videos showing this. Framerate in a fast paced game is crucial to good gameplay
Voice acting outside of Knuckles is actually quite good for a Sonic game, I'll give you that.
Is it a terrible game? No, terrible is what I reserve for a game like Dungeon Keeper iOS. However, the game is still a broken mess of a game in terms of a LOT of stuff, probably not helped due to the rush to get the game out.
At the very least, I do hope BRB doesn't just let this game sit idle. There are some fixes that could be done... and should be done. Basic bugs, glitches etc. I mentioned previously on the forums the game cover mentions DLC... would be curious to see if this idea is dropped entirely. Lost Worlds got it and those devs were pretty good about showing support. BRB... let's see what they do...
There's been a massive Exodus of staff from BRB starting back in September of last year with the game's creative director. I think the company is more of a shell now then an actual game studio.
Honestly, if all those people who are like "DAE OoT and Pokemon from when gaming was good." were to do their research they would know the Wii U is the perfect console for them, and if they bought it, it could put the Wii U in competition with PS4. But people don't like to do research. I still see people complaining about how Nintendo isn't working on a starfox or metroid when they've confirmed they're working on one and heavily hinted at the other.
Ah well. People are stupid.
I'm nostalgic not for the games(OoT is one of the weaker entries in the Zelda Series, where as opposed to creating something new they just went "3D GUYS" and added a time travel element late in development. Conversely, It's little surprise that MM/WW/aLBW are my favourite, mostly because each one picks an idea and executes it), but I am nostalgic for the way the Gaming Community was in a sense. the biggest issues were over what game was better, not about game devs selling games that don't work, or online DRM, or the whole Microtwitsactions trend, or the very idea that 10 MILLION copies is needed for a game to break even. I miss the smaller, more simple, less factory produced AAA games.