GAMER LOUNGE 20XX (NO CASUALS!!)

[Koh]

There's no solution to that issue, though. Mario games "got back to their roots" in the form of New Super Mario Bros, but now that series is panned for lack of innovation.

There is a solution, and it's actually quite easy.  You retain all the things that people actually liked about the games, and add to the formula, rather than just copy and paste the exact same thing and change the levels.

Perfect example being the 2D Final Fantasy games.  If we look at them mechanics wise, the evolution is quite clear; you go from the most basic turn-based combat with minimal customization in FF1, (skip the experimental FF2, as they were trying to find out what else works and what doesn't), to an even more layered turn-based combat system with heavy customization in FF3, with its job system.  FF4 brought in more intricate stories and introduced the more refined turn-based battle system, Active Time Battle, but took away the customization.  FF5 brought it back, better than ever with even more customization through the job and ability systems, on top of having an involved story.

Another perfect example being Pokemon Gen 2. It fixed and improved everything wrong with Gen 1, and added new mechanics on top of what was already there, which became series staples, like the Day/Night system with timed and daily events, breeding, new Types, and so on.

It's easy to innovate and retain what's good about the series, while also bringing new things to the table.  You just have to pay attention to what people actually like most about the games thus far, and expand on them.