Some lengthy games according to my hours logged on Steam (metroidvanias that I allegedly have clocked in over 20 hours on). Some of these run times might not reflect actual gameplay, it's just how long I had each game running on Steam, possibly taking breaks and walking away, but I think most should be fairly close to actual play time. Also, sometimes I take forever to do essentially nothing, or go around checking every tile of a map for secrets and such, because I like leisurely exploring everything while avoiding guides as much as possible.

• Astalon: Tears of the Earth (23.5 hours, 100% completion for main game)
• 8Doors: Arum's Afterlife Adventure (23.6 hours, 100% completion)
• Sundered: Eldritch Edition (24.8 hours, 99% completion)
• Valdis Story: Abyssal City (25 hours, 89% completion)
• Outbuddies DX (25.5 hours, ??% completion, no completion counter, but I beat it)
• Catmaze (26.7 hours, 100% completion)
• Environmental Station Alpha (27.7 hours, 102% completion? I think I used some guides)
• Batbarian: Testament of the Primordials (30.4 hours, no completion counter, but I beat it)
• Chasm (34.9 hours, 100% completion)
• Cathedral (36 hours, no completion counter, but I beat it)
• Monster Boy and the Cursed Kingdom (37.4 hours, 99% completion)
• Salt and Sanctuary (40.5 hours, no completion counter, but I beat it)
• Vigil: The Longest Night (41.7 hours, no completion counter, but I beat it)
• 3000th Duel (49.5 hours, ??% completion, not sure if this game actually "ends")
• Blasphemous (51.6 hours between two save files, 99.95% on one and 15.52% on the other)
• Hollow Knight (96.2 hours, 104% completion... I... do not know why that took so long...)
• La-Mulana (141.5 hours, used just a couple of guides and still have not beat this game)
• La-Mulana 2 (147.7 hours, begrudgingly used a few guides and finally beat this one)

Note: The only game on this list that I definitely have not beaten (defeated final boss or whatever and got an ending) was La-Mulana (3000th Duel seems to let you just aimlessly wander around forever at some point, which was annoyingly confusing, but I think I beat all that could be beaten on that game). The completion percentages provided are for whatever each game considers a completion percentage, I assume most of which are a combination of map exploration and item collection.