Only one Mummy movie, in my opinion, is worse and that's The Mummy Resurrected, which had eerily similar problems to the ones that this had. Day of the Mummy does have one redeeming quality(whereas The Mummy Resurrected had none) and that's the location of the inside of the Mummy's tomb, suitably claustrophobic and effectively creepy. In fact the locations in general are not too bad. But it was very difficult to enjoy them because the movie had such a dreary look and the way Day of the Mummy was shot was highly suggestive someone having the complete inability to keep a camera/video-recorder straight.
Day of the Mummy does use the found footage-like/picture-in-picture idea. This could have worked and could have potentially been creative, but it is way over-used and often at points where it was not needed. To say it was distracting was an understatement, so much so that a lot of the time it was used it took me right out of the movie. The script is incredibly weak, some of it sounds like it was improvised on the spot but most of it sounds like the actors only received the dialogue just minutes before and were reading from cue cards, hence why it was acted out in such an uninvolved and awkward manner. As for the story, there are glimpses of one but there is strong emphasis on the glimpses, what there is of story is painfully predictable, interminably slow in pace and lacking in everything you'd expect for a horror to work(suspense, tension, horror, fun, scares, thrills etc.).
The characters are walking clichés ridden to death, and they are not developed or interesting at all so it's impossible to root for them. To make things worse the acting is awful from actors who clearly did not want to be there in the first place, even from Danny Glover who squints and winces his way through his screen time giving the impression of why did I ever agree to do this. However that he is actually the best actor in the movie is testament to how bad the acting is, William McNamara is a long way from a dashing hero and actually looks bored out of his skull, even the most bored-sounding answering machine has more energy than him. Don't expect the Mummy/monster to save the movie, it doesn't look too bad but it's under-utilised, it acts intoxicated rather than imposing so it doesn't come across as scary at all and it's hard to shake off the feeling of that it's a man in a costume. Apparently the director has prior experience, but considering the ineptness of the direction here that's hard to believe.
In conclusion, awful movie in every way apart from the tomb location. Maybe see it to see for yourself how Glover fares here and how his career has gone down the toilet, otherwise while not quite as abysmal as The Mummy Resurrected Day of the Mummy should have stayed buried. 1/10 Bethany Cox