For Sonic 3 you 'rush' through Angel Island Zone but this time you only get to fight two bosses. Those being the Angel Island Sub-Boss and Main Boss respectively. Oh, and they reuse an enemy from the Sonic 2 game instead of making a new one!
Finally, Sonic & Knuckles (who can't climb walls by the by) we go back to three bosses as you traverse through Mushroom Hill Zone where you fight their Sub-Boss, Boss, and then the Flying Battery Zone Sub-Boss. Oh, and this game got three new enemies!
Now if you watch the videos, you'll see these games are horribly slow (so much so they sped them up for commercials) and the graphics are iffy.
However, awesome people in video game preservation HAVE made them playable! http://hiddenpalace.org/Official_game.com_emulator_and_debugger