I viewed this recently, and it has held up extremely well considering it's age. Essentially this is a 'SUIT-MATION' delight, and in the light of today's over-used, over-familiar sterile CGI monster effects, it is refreshing and reassuring to see good old-fashioned hand-crafted special effects.
The story darts along at a brisk pace, edited so that not a minute of boredom is evident on-screen: this is far better constructed story-wise than the majority of this type of film. Stock footage of warplanes and ships may not be brilliantly matched, but somehow seem to add to the vigour of the piece.
Uneven matte-work and bleed-lines pop up now and again, but this never marred the '33 'KING KONG' either, and indeed I can now spot 'sophisticated' greenscreen composite shots in many expensive effects films from today. This movie is much more entertaining and engaging than the 1976 'KONG', which wasted much of it's huge budget for various reasons too detailed to go into here.....'GORGO' delivers far greater spectacle and entertainment on a far lesser budget, which was put to infinitely better use.
I enjoy the similarly 'GODZILLA' films too, but in all honesty I prefer the relentless dynamics of this vital and impressive MONSTER-FEST.