Julian Fellowes' Titanic drama has received largely lukewarm reviews from critics after Sunday's first episode aired on ITV1.
Writing in the Daily Telegraph, Sarah Crompton said: "There was both too much and too little to concentrate on, and no-one to care about.
"If I were forced to judge Titanic on this one episode alone, I'd call it a damp squib," she continued.
The four-part drama coincides with the centenary of the liner's sinking.
Ms Crompton added: "But having seen part two, I can assure you it gets better."
It stars Linus Roache, Celia Imrie, Geraldine Somerville, Toby Jones and the newly announced Doctor Who companion, Jenna-Louise Coleman.
The mini-series has been generating huge interest following the success of Fellowes' Downton Abbey on both sides of the Atlantic.
And it attracted a strong audience, beating the final episode of 1930s drama Upstairs Downstairs on BBC One, which aired at the same time.
Upstairs Downstairs had an average audience of 4.4 million, while Titanic's average was 7.4 million, according to overnight figures.
Times critic Andrew Billen said that he struggled with the speed of the opening episode.