The Mummy is like the White Album. As a youngster, I found it too old, too strange and out of touch with MY world (The Omen, Lost Boys, American Werewolf, Phantasm, Grifter Bikes, Jet Set Willy) to really get into it, to really understand it's beauty. But over time, as I became more mature (maybe not mature - older then) I learned to truly love and appreciate it. I still wish they hadn't let Ringo sing that song about being in a car crash and losing all his hair though. That last sentence applies to The White Album only.
The Mummy is a haunting, romantic classic from a bygone world that we can only catch glimpses of through monochromatic ghosts - feel the breath of the dying silent-movie era on its shoulder as it weaves its hypnotic spell.
Not sure where that last sentence came from. Anyway, The Mummy, as I've said, is a romantic story - with many, many plot similarities to Universal's Dracula movie of the previous year. In both, we have a romantic undead anti-hero trying to get his undead hands on a beautiful heroine. The beautiful heroine's proper human beau (not undead) pursues his undead love rival with help of a talisman, and a wise old expert. In Dracula, it's Van Helsing, in The Mummy, it's Dr. Muller. In both, it's the legendary actor Edward Van Sloan playing the part.
Karloff dominates. His make-up (courtesy of Jack Pierce of course) is magnificent, both as 'The Mummy', and minus the bandages as the sinister but apparently human Ardath Bey. The make-up on the latter is beautifully understated, subtle and spot-on. Somehow he looks like a guy who's been stuck in the sand for thousands of years. And he's bloody scary looking. The POV shot of him 'working his mojo'(or the Ancient Egyptian equivalent) is an iconic image...

... and you won't find many of them in the 1999 'version'.
What more is there to be said? If your last memory of 'The Mummy' involves Brendan Fraser battling 'The Rock' then you know what you need to do. Relax, sit yourself down and take a step back in time... to one of those that they just don't make any more.