I tend to disagree , its the damn level to blame for the bad impressions , that sci-fi crap is an anticlimax of what serious sam stood for , if you would go to EXTRAS , CREDITS you would see scenes from other levels that remind of the original SERIOUS spirit , allthough much has changed.
And it runs slow because its a new game with modern graphics , im sure that the first serious sam when it got out it needed some SERIOUS hardware - for that time...
You must play tha game with an open mind . A bucket of crap its not , and if it were i would still play it for the funny catchphrases like "Damn its cold , my nipples are like pencil erasers.."
P.s.: The supercanon is not as spectacular as before , canonballs are "lazy"...
