hmmm. . . My favourite game would have to be Sonic 3 & Knuckles (sonic 3 locked on with Sonic and Knuckles) yes it might be cheating considering the two are stand alone games, however they were at one point a single game that simply became to big to be able to contain on a single kart, so Sega compromised. A lot of people say Sonic 2 is the best 2D sonic game, however I always though they took all the good things about Sonic 2 and added on it with 3, it has my personal favourite levels (Carnival Night and Lava Reef) and some of my favourite bosses (Launch Base boss and Death Egg boss) not to mention the implementation of elemental shields. All in all this game is hands down my favoutie platformer and one of my favourite games of all time.
Another game I love in Gunstar Heroes (for the Genesis) simply put if something on the screen isn't blowing up, you're either dead or doing it wrong. One of my all time favourite run and gun games.
I have a lot of games I hated, too many to recollect at the moment but one that keeps popping into my head is Sonic Spinball. Wasn't made my Sonic team but rather the American technical staff and because of which took elements from the comic book and animated series, which I never really liked. The game is a solid pinball game i'll give it that but in many cases it just felt cheap to me, the first level was fine but after you finish it the game just seemed to be finding ways to constantly make you waste time with constant backtracking where you always had to worry if you were going to be thrown into a chute that took you back to the very beginning of the stage or worse. the bosses were very unimaginative and were either too easy or unbelievably cheap. The final boss however is the reason I trruely despised this game, I had this when I was about 10 years old and never was able to finish the game until I bought the mega collection on steam last year, and using save states I was finally able to beat this guy. Even with save states it took me over half a goddamn hour to beat the final boss. Why, because the boss took an unbelievably large amount of hits to beat coupled with the fact that you had to do a convuluted and never explained sequence of other button presses in order to make him vulnerable enough for a few moments needed to bounce up and hit him, coupled with the other fact that his major form of offense was to throw you out of the boss area all the goddamn way back down to the beginning of the stage. It took me over half an hour to beat this guy constantly using save and load, I'd imagine if I didn't have these tools I would have played RPG bosses that took less time to beat, and were probably less frustrating than this boss. . .