Explormers* - known elsewhere on the internet as Metroidvanias, Castleroids, or JumpyFindyMapExpandies - are extremely my shit. I've long been trying to put into words why exactly that is, and my usual pitch is that these games frequently combine my love of 2D platforming, the keeping notes and updating maps more common to CRPGs, and the many varied approaches to level design that results from gating off specific areas based on necessary upgrades. That there's so many games being made in this specific model speaks highly to how compelling it is, and even if their developers start running out of ideas as market saturation hits critical mass I'll still probably never get tired of playing them and meticulously exploring their every dead end.
With the following list of Explormers What I've Played, I've tried to highlight the most exceptional or unique aspect about each one. It's easy to think of these games moving off a production line with the volume that are released each year, but the majority of developers creating these are always looking to put their own spin on it or emphasize different facets of the platforming/combat/exploration/puzzles/character development paradigm that they appreciate most. I've also put this list in chronological order, to better demonstrate how much the genre has grown.
And hey, not to put too fine a point on it, but if you happened to need the distraction of a few giant maps to explore at the moment I hope you find some inspiration here. (And be sure to contribute your own suggestions in the comments; I'll have a master list of those I've yet to try going on too.)
*I recently saw a new explormer on Steam refer to itself as an "explor-action" game, and... damn, that might be a better name for them. Steps around the "not a platformer" issue some of the below games have, like Aquaria and Insanely Twisted Shadow Planet.