The Terminator series is up there with Star Wars, as one of those film series in which the second film is pretty much the pinnacle of the series (Which, actually, applies to the original Star Wars trilogy and the prequel trilogy both, if only because The Phantom Menace remains one of the most awful pieces of cinema ever put on film -Ed).
With the perplexingly named Terminator Genisys being the fifth of the time travelling murder robot films, I don’t see a great deal of danger that the crown of Terminator 2: Judgement Day will be under significant threat.
That said, it does leave a rather wide scale on which Genisys could still fall. The Terminator was good, but not as good as Judgement Day. Rise of the Machines was off the chart awful, whilst Terminator Salvation was not as bad, or okay, depending on whether you mentally sub the ending for what it was originally going to be before US test audiences got a hold of it.