What's your favorate 2D/ 2.5D Sonic games?

I always just go to Sonic Mega Collection Plus. But there are some that aren't even on this game. Such as Sonic CD. Or Sonic Episode 4. 

Mega Collection Plus. On one offically licenced PS2 game you get most (maybe all?) Sonic games that originally released on the Segs Genesis and Sega Game Gear. 

Including Sonic 3D Blast -genesis- and Sonic Drift -gamegear-

I don't know of any other offical Sonic game bundles that come close in one collection. 

Sega went the extra mile and even included *some other Genesis games youd have to unlock.

i favorite is def Sonic's Ultimate Genesis Collection for the ps3 since that's what i used to play for the most part.

I remember wishing it had sonic cd included in it lmao

I wish instead of going for Full 3D Environment.

Sega's Sonic Team just went with 2D Sonic Game with nicer Polygonal Presentation for their Mainline Sonic Game on Sega Saturn like what's seen on "Clockwork Knight" with Futuristic Stages and other stuff and work on it the same time as Clockwork Knight and release it in Early 1995 and have it prepared for North American and European Sega Saturn Launch and call it "Sonic The Hedgehog 4" or "Sonic S".

Then test the waters with "Sonic X-Treme".

Sonic Advance trilogy rocks hard. Also Sonic Rush

Sonic Advance and advance 2 ! I always loved playing it as a kid and loved playing as cream 
I wish I had a chance to play sonic rush because Blaze is one of my absolute fave characters SOBS 
Sonic mania was just as fun for me too^^

Today I just bought Sonic Colors for the ds it was unexpected but I forgot that was also a 2D Sonic game I remember playing the demo in 2011 off of the Nintendo channel on the Wii. It would send the demo to your ds through download play.

I mean very obvious choice, but Sonic 3 and Knuckles is the pinnacle of not just 2D sonic but just in general, I think it's the best Sonic game to be made. CD is a close second, but I've also really enjoyed Sonic Triple Trouble and the first Advance game. Been meaning to get around to the other 2D rush games (Sonic Rush Adventure, Colours DS, Generations 3DS.) but I enjoyed what I played of the first Rush game, it's just I personally prefer the level design of classic sonic for my 2D sonic game, while preferring the boost formular in 3D sonic games

Gotta go with mania. Easily my favorite 2D platformer ever. What it lacks in completely original level themes it more than makes up for in design, gimmicks, and visuals for those re used themes. I honestly think the mania versions of those levels are better than the originals in most cases, something like flying battery zone especially feels like a new level completely. And the 4 new zones, some of the absolute best in the series, studiopolis alone would have been an amazing standout, but we also got mirage saloon, press garden, and Titanic Monarch. All of these have such unique themes for the series, along with the amazing visuals that really bring the places to life. And the music for these levels my god, just go listen to them, and hell the whole soundtrack, because words can’t do it justice. It’s so rare to have a game that was obviously made by people who are huge fans, but isn’t designed just for fans. So many people I know who aren’t huge sonic fans have played and absolutely loved the game. While not the most original or groundbreaking, to me its the absolute best classic sonic gameplay can offer.