Whatever was lacking in special effect was made up with suspense and good timing. There’s a reason many of these are considered to be classics, the remakes were just a bad attempt to make these movies more current but instead ended up ruining them with CGI and absolute lack of actual soul. We wish they just left these movies alone.
If we asked you to name the best robot in movies you would think it would be an easy task right? But when you actually start to think about it there are many many great robots in movies. Nearly every great sci-fi movie has a robot in it, most are truly awesome too.