Did you get the Crystal Key from Solberg (the wizard who lives off the river in the North East, near the Nephil fort where you had to get the necklace)? As soon as he tells you about it you can get it, but he advises you not to take it until you repair the Demonslayer. I thought you said you talked to him, but did you actually take the key? I think that’s what lets you through the barrier that you’re talking about. Check your inventory even if you think you have it.
Get the Demonslayer fixed before you fight the demon in the tower. I think you can kill it without the Demonslayer, but it will be harder.

I use both Steam and GOG, but I usually only use GOG for stuff that’s not on Steam. I keep forgetting to try and get my computer fixed.

Yeah, The Last Door intro is a tutorial, but it’s also a great intro.

I Have No Mouth is great too. I just reread the short story a few weeks ago.

I’ve heard of Alwa’s Awakening but I haven’t played it.

I think I’ve played all the 2D Metroid games except Samus Returns, the “official” Metorid II remake. It can’t be as good as the illegal Metroid II remake, probably my favorite game that I’ve played for the first time in the last 5 years. The Last Door is up there too though.