Thank you very much (for the feedback, following and gameplay). I will watch the gameplay and analyze it. I respect the critic on Metroid-vania-ness: I think I could have done more stuff like placing blocks which can only be destroyed with the "shotgun-frog" and similar stuff.
As of now I am definitely planning on further developing the game, but make a small pause during the holidays to get a more "neutral" view onto what I am doing.
In terms of minimalism: the idea was that the player has no ability and sort of "gets" abilities by carrying item. But that clearly has the downside of the player being difficult to balance. Next I want to add a feature for "throwing" items to make carrying stuff more fun.
I am excited myself to see where the project is going, since I have many ideas which need to be sorted. If you have any ideas for interesting features: please let me know!