To me, Heretic is not 'bad', but it's still lacking in many ways.
I'll give some anecdotal evidence: I played Doom (2) and enjoyed it very much, to the point that I have some residual memory of pretty much every map in the game, even 30 years later.
Now with Heretic, I've played through all five episodes at least once (a LONG time ago) and the only maps I have any residual memory of, are part of Episode 1 - the shareware episode, and the boss fight at the end of Episode 3. Everything else is a blur, and I'm not interested in revisiting any of it ever again.
Compare that to its 'sequel', Hexen - where I can, again, make recollections about pretty much every map of the game, all these years later.