Unless you dislike silent films, really the only concern here is making sure you get the best of many versions. As of 2/2015, the best version to pick up is the KINO 4K bluray. All except one reel is from the original negatives, and the missing reel is remade from a mix of the best remaining print versions available. The monochromatic colorization process chose colors based on the earliest remaining print versions (from South America of all places for a German film).
At 77 minutes, this was a long movie for the time, and despite some imperfections remaining in the film quality none are ever too distracting, even on 50" modern TV screens. The clarity is very good, and reveals details in both faces and set pieces I had never picked up on before in older versions. Given this was a visual work, it almost seemed like I was watching it for the first time. The monochrome colorized acts, some where everything is blue, sometimes everything yellow, sometimes pink based on time of day, location, etc. look great.
I'll let others describe the details of the plot, but basically this was the first "German expressionism" film and came out around 1920, with a spooky, carnival side-show vibe. The set was very intricate for the time and highly stylistic, with odd angled buildings, lots of shadow, and various disjointed features that look like something Tim Burton would have done if he was alive then. The movie is subtitled and has options for two different musical scores, one from the time period and one new. Starts a little slow but with a great ending, one which seems surprisingly sophisticated for the time but just probably means we are a little snobbish in how we think about the past today.
Bonus features are awesome. The booklet is not to Criterion standards, but is still very nice. Includes a still gallery that has some original movie posters, and most impressive is a 52 minute German (english subtitles) documentary that while highlighting the film also touches on a dozen others and is chiefly about the post World War I impact on German film making. Well worth every penny.