When looking at the VGchartz numbers of Sonic the Hedgehog 3 on the Sega Genesis it's strange seeing how the previous game (Sonic 2) sold roughly three times it's units. Not that it's unprecedented for games to sell less than their predecessors but even bad sequels can manage to sell more than a third of the last game. Sonic 3 may not be as good as Sonic 2 but as far as sequels go you could do a lot worse.

There's no doubt it has to do with Sonic 2 being a pack-in game for the Genesis during 1993. So why were Sonic 1 & 2 bundled but not Sonic 3? It could be that they didn't think it could compete with Super Nintendo's Donkey Kong Country bundle. It might also have to do with them transitioning to 32-bit consoles around that time, potentially ending Genesis' life cycle.

Some guy working at The Great Escape told me the reason Sonic the Hedgehog 3 was such a rare cartridge over there, was because Sega did a low production run of it. Because with Sonic 2 they over projected it's sales, leading them to manufacture more copies than they could sell off in a reasonable amount of time, thus leaving them holding a bunch of inventory and they didn't want to be burned like again.

Though, since it's mostly anecdotal, it doesn’t qualify as a reliable explanation. However it points out the difficulties involved in manufacturing cartridges, which took longer and were more expensive to make than discs. – In fact I think there's a good chance that other game companies had issues with this. – Regardless, it still leads me to question how well Sonic 2 was selling before they bundled it.

Sonic 3 was a good game, but imo it was a bit more difficult than Sonic 2 and 1 which made it less desirable for kids who like the simple jump and run of the Sonic series. Sonic 3 featured a bit more complex level design.

man that Carnival Zone act 2 was the WORST gaming experience of my childhood! i never finished Sonic 3 back when i was a kid because of that damn block thing!

Sonic 3 had some really nice elements, Knuckles was awesome, Angel Island was stunning and the music was excellent. but it was just too damn hard imho. and Sonic 2 was a tough act to follow!

in my personal opinion, the junction with sonic 3 with sonic and knuckles is the best sonic experience.  sonic 3 by itself is kinda dull with only 6 levels.  hyper sonic and knuckles and super tails is just great.  sonic 2 is still great and i can see why it sold so well.  it was a brand new experience for gamers at the time.  i never was a big fan of the first sonic.  im not sure why sonic 3 didnt sell as well as sonic 2.

Are we talking about that dead-end room with the spinning cylinder? That took me ages to figure out, until I found out that you could move it up and down with the D-pad!

Bundling aside, its possible the Sonic games saw a decline in sales due to lack of interest. The core games are all kinda the same.

Look at Donkey Kong Country on SNES. All three were much the same and sales saw a huge drop.

A franchise like Mario on the other hand often tried something new.

I just found that out last month... after I beat the game like 10 years ago. I remember it taking me hours of re-doing that level and each time I get to that room i'd time my jumps on that thing and when i get it low enough, jump off. Took me like 5 mins out of the 10 that you had for the level each time I actually did make it. Most times, I'd clock out and have to start over...

Not only was Sonic 2 a pack-in, but it was a pack in for about 2 years straight here in the US, from right after the game's initial release in '92 right through holiday '94, and wasn't replaced until SEGA released the "6-Pack" of classic games in '95.  That alone is why Sonic 2 sold a bajillion copies.

Plus, Sonic 3 was basically broken up into 2 games... Sonic 3, and Sonic & Knuckles, which came out just 8 months after Sonic 3 was released, so that effectively split the sales of each game.

Weird, growing up, I thought Sonic 3 was the easiest of the 3. The first one I still find the hardest. I just played through 3 last week. Always my favorite!

Man i miss Sonic 3 and Sonic & Knuckles, Knuckles was the last good new character..it all went downhill from there

Aside from that one room in Carnival Act 2, It's the easiest to me as well.