Thanks for the comment!

As far as I know all levels have exactly 3 keys. Is it possible that the other keys were just unidentified (the "???"s)? It's not impossible that the level generation has a bug somewhere, but I haven't encountered any issues with number of keys.

Music and sound effects are definitely high on the list of things I'd like to add whenever I get around to releasing a post-7DRL version.

In terms of difficulty and luck, that's also been my experience playing through it. It's winnable at least some of the time but there's a large amount of variance in difficulty depending on what combination of enemy types you run into. At a minimum, I think it was a mistake to have a random number of links per level. If you've got multiple next levels to choose between then you can skip the worst ones but currently the level generation sometimes only generates one option.

The next major change I have planned is probably going to make the game significantly easier (I want to give the player access to limited use special abilities, but ran out of time to include them in the 7DRL version). I expect some of that to be offset by compensating difficulty increases elsewhere, but if nothing else it should give you more options for getting out of bad situations and/or avoiding getting into them in the first place.