This topic has been beat to death, true. But my two cents worth:
Cent 1) One of the most notable flaws of this game when it was reviewed by InQuest was the lack of any "comeback" ability; that is, once you started losing, there was very little you could do about it. Other CCGs have ways you can pull a victory from the Jaws of Defeat. Not so Spellfire.
Cent 2) I recall that TSR created eleven (11) expansions for this game before they finally shut it down. That's a lot of support for a dog. I would say this reflects the fools in charge of TSR in those days, more than it is a comment on the viability of the game.
BTW, I can get Spellfire Boosters cheap. Who wants them?
Centurion