Visual simplicity, when done well, can absolutely work. In the case of Gum+ I wouldn’t say that it necessarily made completing its very classic box pushing puzzles terribly harder, but it also did nothing to distract from the fact that it feels like very thoroughly trod ground without any real flashes to help it stand out. You’ll be grabbing blocks of various shapes and sizes and then carefully moving them as efficiently as possible around obstacles to get them to where you need them, usually dropping them into place to allow you to reach the exit but there are also times where you’ll need to carefully be sure they’re not then in your way. I wouldn’t say it’s really any less thrilling than most of its fellow box pushers, honestly they’ve all become a bit stale at this point, but without at least a flourish of added complexity or some visual reward to keep you engaged it also ends up having too few positives to really try to elevate it at all.