As for my contribution to the thread, I'm going to pull out one more example that follows the same path: Mega Motherfuckin' Man 2. MM1 acted as the proof of concept -- give the players a choice in how they play the game, include pinpoint platforming controls, a simple weapon that can defeat every enemy in the game if the player has enough skills, but give them more weapons to ease the game for those who don't want to do that. Offer dozens of way to beat the first half of the game (Do I beat CutMan first, or GutsMan? What if I go for BombMan, he's easy enough. ElecMan? Nah, 'cause then I have to go back for the item. IceMan? He's incredibly difficult to dodge... hmm...), then once you have all of the weapons, funnel them all into the same fortress and force each player through the same set of trials before facing the final boss, to weed out the ones who got there by luck.
There were a few flaws with this model. Some of the puzzles were too "random" (I'm looking at you, floating fuckin' platforms in Ice Man's stage that didn't follow a set path). There was one item in the game that was necessary to beat the game, but you might not have grabbed during the course of your playthrough. The bosses were too unforgiving -- some bosses could beat you in three hits, which frustrated the fuck out of casuals.
Enter Mega Man 2. Include two more bosses and three more items in the game, plus some Energy Tanks in case you get all fucked up along the way. Most of the levels are larger and slightly more involving, and it includes a couple of instant-kill spots just to make things a bit more interesting. The weaknesses are a bit more linear and obvious (for the most part), and while the bosses don't hit quite as hard, they take more hits to kill themselves, balancing things out a little bit.
There are also three items in the game now, all of which will become necessary after the halfway point in the game. This time, however, you receive them during the natural course of the game, meaning no one is left out of the loop because they didn't find/go back for an item. Wily's Fortress is larger, the bosses feel more like "automated defense," giving the impression that you're breaking into a fortress. Also, while you still have to revisit the bosses later in the game, you now have the allusion of choice about which bosses you want to take otu first, and it takes the onus off "HA HERE'S A BARRAGE OF BOSSES THAT CAN ALL FUCK YOU UP IN THREE HITS" and more "here's a series of challenges, all of which can be beaten, but we'll give you a breather in between just in case you fuck up, 'cause we're bros like that."
Again, there's a graphical upgrade (things look sleaker, and the levels "pop" more in terms of colours used, and in particular the background animations in levels like Quick Man and Metal Man), but it's not as huge of a leap as between SMB and SMB3. But that soundtrack... holy shit. Easily one of the best soundtracks on the NES.
This game was just a huge improvement in every way over the first one, and is truly what started the Mega Man craze back in the '80s and '90s. The series wouldn't really ever take a huge leap forward again (it would take a number of small, "safe" leaps throughout the next couple of years). That all changed with MMX, which is arguably the best Mega Man game ever made, but
better people than I have explained why it's such an amazing game.
I'm tired of typing now and don't have a way to close this topic. I had Chinese and rainbow sorbet for dinner. It was very good. I'm also very glad the Toronto Maple Leafs are still in the Playoffs, although I feel guilty as shit for saying that. Have a nice night, y'all.