It would be difficult to say precisely because the results that you describe are usually due to an inadvertent (and often undiscovered) mistake, but:
Not using a ricer or mill could cause you to inadvertently over-work the mixture; by the time you feel like you get the right tactile response it could very well be over-glutenous (this explains the chewy center). If your budget permits, even a cheap ricer or small mill would help (they're found for as low as $10), if not, just try mashing with a fork until fine prior to mixing with the flour and egg.
You need to be somewhat aggressive with salt, as others have pointed out. Twice as much as you think you need might seem like a lot, but try that as a general measure.
You mentioned blanching, did the water come up to a rapid boil very shortly after losing heat when you introduced them? You might want to use a higher-output burner if not. This can also be the bane of some fresh egg pasta; the water needs to be at a steady rolling boil and recover quickly. To compensate, you can use a bigger pot with more water and boil it covered, it might recover sooner. This could also be why they were a bit chewy
Those points could also be contributors to the taste you describe but the sum of the ingredients matter here, too. How old was the flour? With pasta and gnocci, I use a brand that's clearly marked with a packaged date so it can be rotated properly.
Also, did you groove them? Little grooves on the sides help the Maillard reaction so they don't need to fry as long, which keeps the oil from going pungent, and helps hold the salt a little better.
Source: I've screwed up more Gnocchi than I've gotten right. It's a labor of love, and so rewarding when they come out perfectly. Don't give up!
