I think that has more to do with overly ambitious predictions than film quality. It may have done just fine but if they expected a Transformers level of money grossing with it, of course it'll look like a flop. I don't think any Terminator film is ever going to be a huge success like the original two, you can do better than 3, which T:S was, but sci-fi seems like a genre loaded with over the top effects and creations and not given much story anymore, not like the used to.