That’s my feeling too, “back in the time”, sequels were feeling like an evolution of the previous game : new character design, enhanced visuals, and most of all, much enhanced (sometimes completely different) game mechanics.
Nowadays, most AAA sequels are just asset refactoring, hiding behind “branding preservation”.
Look at those screenshots :
First one is ToeJam Earl, a 1991 Sega Genesis game. A top-down view gameplay, where you had to wander through space to find out your missing ship pieces. There were christmas gifts spread all over levels (which were totally random generated, as a sidenote). You wouldn’t know which effect would be triggered by each box until you used it. Some were good (speed boost, spring shoes, rocket shoes, buoy to go on water, etc), and some were bad. Added to that, the content of each box type would be randomized at each new game.
Enemies were totally random too, fun as hell, each having a different attack/effect on you. Like a hawaiian dancer who would stun you by making you dance for 5 seconds, or a fake mailbox (as there were true mailboxes where you could buy gift boxes) that would turn into a monster as soon as you try to approach it, or a Cupidon baby that would trigger some arrows at you, etc.
The biggest fun in this game was that you could coop with a friend, splitting screen as soon as one was going too far away.
I had so much laughter with it besides my friends, we’re still cherishing its memories at times.
There were totally random moments, like when Earl, the second protagonist, would randomly lose his trousers for no reason. Imagine that happening when you were with your friend trying to make a way through a horde of enemies …
Another fun game mechanic was that enemies could fall asleep when nothing happened around them. You could tip-toe by pushing A, passing next to them without waking em up. The fun stuff was that randomly, your char could suddenly ATCHOO while tip-toeing … I’ll let you imagine what would happen.
Basically, there was a true will to create new things. New mechanics, new designs, for the sake of fun. A game that came out of nowhere, and took everyone who played it by storm.

Second one is ToeJam Earl 2, released on the same system, in 1994. The dev team radically changed their approach to gameplay, and even to graphics. Everything was a global overhaul. There was a huge risk to piss off fans who wanted something “just like” the first episode, and I admit the game was surprising at first. But they took that risk, and it was a blast in the end. Different, but still good. That decision to change everything didn’t even come from gamers, it was all dev’s initiative, “just because”.
Everything was more oriented towards a shooting side scroller, based on agility and precision.
Gift boxes were gone, all enemies were totally regenerated, gameplay wasn’t top down anymore, but side scroller, and coop was more skill based. But it was still (differently) fun.


And even ToeJam Earl 3, appeared on the XBOX many years later, took yet another different gameplay approach (full 3D), and that didn’t prevent it from being a success.
Now, here is Gears of War series, which I guess doesn’t need any comment :
GoW 1 :

GoW 2 :

GoW 3 :
