Tony Scott is behind some of the best movies ever (read: True Romance, The Last Boy scout and Top Gun) and this is of course something to keep in mind. Deja Vu takes a quite serious Sci-Fi theme and turns it into a pretty good movie - half serious, half entertaining. Denzel plays his role really well. However the movie is filled with trivial things and action sequences that is there only to "keep us going" and is not really needed for the story. While this is quite ok, it does take the movie down from being a classic.
The general feel that the movie gives us is a good thrilling feeling and we can't really know if things will be good or not (if you didn't watch the trailer that is... bummer). When looking through the triviality we are presented with a deeper story about love and about changing the future and past for the better. Even if the obvious glitches like the "time machine" and the projection of items are totally unrealistic I think that this is what the triviality cover up - so that it feels like the "time-machine" a totally sane idea.
In the end I must say I enjoyed this movie and so will you.