This is a very clever adaptation of the novel 'I Am Legend' by Richard Matheson. Even the film's title shows some of the thought that has gone in to it - Omega is the last letter of the Greek alphabet, so the 'Omega' Man is a clever way of saying The 'Last' Man.
Many comparisons are now being made between Will Smith's 'I Am Legend' and 'The Omega Man'. For me 'The Omega Man', even with its faults and the fact it is now nearly 40 years old, still stands above Will Smith's new version. Why? (1) The plot - The Omega Man to me is a far better more rounded and believable story. Especially the ending. (2) Acting - Charlton Heston seems far more viable in the role. (3) The creatures/infected - In Will Smith's version, they are obviously just over the top CGI and behave very unrealistically.
Of course there are problems with the film, but putting these aside we have what I believe is a great 70s cult scifi film, which the more recent 'I Am Legend' fails to match in most ways. When will Hollywood learn just throwing money at a project (and its effects) is less important than the script and its portrayal. Or more importantly, when will the ticket buying audience...