Due to the fact that in 1976 there were no CGI I felt that the movie was quite watchable. The studio productions were very good and very elaborate. The background effects were very believable and always appeared as if they were part of the whole set. The actors did OK considering the premise of the film being set in a type of Jules Vern atmosphere where imagination and possibilities of future exploration were at most improbabilities. Had I watched this film in 1976 I probably would have been in awe of the ability of man to build a machine that could travel to the earths core. I still wonder to this day why we are not all flying around in our cars but I digress. McClure and Cushing have their funny moments, mostly from their facial expressions toward each other which of course makes the film somewhat campy which I loved. The 'monsters' left something to be desired but the story had a good premise although I feel as though some other sort of 'thing' could have been more believable under those circumstances. All in all quite watchable for its time and fun now.