One of the reasons why I love teaser trailers so much is they do just that- tease. Giving the audience just enough info. While a good trailer can sell a movie to the unknowing audience member, a bad trailer can ruin expectations and even worse, spoil a crucial surprise the director has in store. The marketing for Terminator 2 is an example of just how effective the former can be and just how bad the latter can be.
That card up Cameron's sleeve is a scene in which John Connor is being tracked by the T-1000. Ole Arnie walks around the corner, whipping out a shotgun and stepping on roses. Up until that point we only know him as a man who scuffed up a group of bikers in a bar. It's a trick that relies on us as observers of a deadly game of cat and mouse. Relying on our knowledge of the first film in which Arnold was a baddie. Without any knowledge whatsoever of Arnold actually being the good guy. As a kid I thought "It's over. John Connor is finished" Only to have the rug pulled out from under me. It makes that scene and everything that comes after worth it.
As for the actual villain of the film, the T-1000 presents itself as the one fully realized computer CGI character (with the exceptions of the Dinos in Jurassic Park) that has ever demanded my full attention. The ability of villains to appear in undefinable forms is something that, while old as a concept, is made new with a fresh coat of special effects wax. The model for the villain here is a police officer. Yet what striked me as a kid watching this movie was it's ability to morph into so many other sharp objects whilst maintaining a distinguishable (and at many moments, chameleon- like) identity.
In terms of being a sequel, it gives us everything we want and more. In fact I'll go on the record as saying, it's the last time an action movie truly brought the goods in all departments. We didn't really need to see the most complex screenplay written within an action film. It's the execution of taking a script penned by Cameron and William Wisher and wincing every nook and cranny of it. Judgment Day is the type of action film that steam rolls across the bones of other so called "sci-fi action films".