Seems fair then...I did sadly spoil myself a bit, but I'll give a shot at this impressions thing. (Basically I'll just pretend I don't know what I know...AKA what I thought about Mania yesterday...)
The game looks pretty dope so far! I'm not as hyped as everyone else, given that Freedom Planet is my current favorite game and its probably not going to get topped soon. Sonic Mania will most likely be somewhere in my top 15 though... (I tend to like games that are hard and fast anyways so suffice it to say despite having a lot of nostalgia for Sonic 3 its not what I consider the pinnacle of gaming/platforming).
I could do without the nostalgia pandering though, I do like what I'm seeing in the Act 2's (especially CPZ) and the new zones though. (Hopefully we get more imaginative new zones in the game aesthetically) The level design is the perfect mix of CD and 3. As someone who likes CD best and has 3 as a close second this is quite perfect as an "official" sonic game, it could be better than any we have had so far! (that's not too hard now that I think about it though)
As far as being better than fangames, we'll have to wait and see, my favorites are Boom (sonic 2 hack), Eggman hates furries and Sonic Erazor. All very short but have really good level designs and physics.
What makes mania stand out I guess is that it will be a finished game. Most fangames sadly aren't like that. Time Twisted which was worked on for 12 years is finished, but I had hoped it would be better, here's to hoping Mania is better!
And onto what I'm known for being nitpicky about...
...the music...
...
It's...okay I guess. Like yes its good, especially the special stage music (and the initial trailer music). But aside from that nothing has really shocked me and made me go "Wow! That is awesome/breathtaking!". Though as of late Stardust Speedway is growing on me. (Can't wait to hear Act 2 wink wink) I want something like THIS dammit:
ahhhh! It's a mastapiece!
Anyways, I also like how the artstyle is heavily inspired by Sonic Nexus XG, which reminds me of yet another masterpiece worthy song...
Gosh darn it I want music like this!
Oh well, I'm probably too picky about this anyways...
Last nitpick...
Sonic's model...eh...I just wish it was the sonic 3 one, but that's probably my bias talking right now!
Sonic Mania is going to be the GOTY for me most likely, not because its noteworthy for me, but simply because I don't think I will find anything else better to play!