My only real complaints with Creature are the repetitive, easy, and fairly high value left ramp combo, and the random distribution of modes. In casual play the latter doesn't matter as much and wouldn't be a necessary change, however in tournament mode that should absolutely be removed. One player getting a pretzel and the other getting Unlimited Millions is just flat out unfair.
As far as the left ramp combo issue, the left ramp should really be given a use in main gameplay rather than just being looped over and over. Hell I'd rather it just do nothing instead of what it does now.
Anyways, other than that I think Creature from the Black Lagoon is one of the strongest Williams games. There's great value in the simplicity, challenge, and replayability. The multiball being only two ball with no add-a-ball is a fantastic challenge that really makes you play in a much more safe, controlled, and protected manner, where losing one ball means losing out on the massive prizes that lie ahead. Most modern multiballs with tiny jackpots, very long ball savers, and add-a-balls that provide even more long ball saver fail to recreate the intensity and excitement that Creature from the Black Lagoon presents. Even the glitch with the multiball playfield multipliers makes for an incredible asset in your game strategy, it's spectacular and wasn't even intentional!
Also as far as theming, atmosphere, sound, lighting, and animation, I find it to be one of the best games ever made. Very, very little I'd want to change with this game.