So, Titanic is bad because some scenes are cheesy nowdays? Then i guess many film classics are cheesy too.
James Cameron is a great director, might not be on the same level as some "auteurs", but he absolutely delivers at what he intends to. Titanic and Avatar were technical marvels with strong formulaic scripts, aside from a few head scratching stuff like "unobtanium" or "I think this ship might actualy be sinking", they were well written and well constructed. They definitely don't have major script flaws of the likes of Transformers or the Star Wars prequels, even if the internet sometimes seems to try implying that.
Funily enough, the criticism Avatar and Titanic get is similar to the one received by Sound of Music and Doctor Zhivago back in the day, where a majority of the public loved them, but film snobs constantly dissed on them, even though even the critics who disliked their pacing or plots considered that they were technical marvels.