It's not nearly as bad as people make it out to be. The only real issue is that there's not as much to do as in Sky once you beat the game. Though in my case, what there is to do has held my interest far longer.
The gameplay in Gates is more polished then in Explorers, which might make the latter a little annoying to play if you choose to play the former first. The things I like most about Gates in that regard are having access to shortcuts for all four of your moves (You only have one in Explorers, meaning you need to open the menu whenever you want to use a move that isn't set to a shortcut), and your walking speed in dungeons is much faster then in Explorers, where it felt needlessly slow to me.