Lijiang is a must-see for any China trip, and of course there is plenty to do while you are coming to Yunnan even from Lijiang itself. Most people do a Dali -> Lijiang -> Shangrila tour and maaaybe, like me, a sidetrip to Lugu Lake which nowadays also has an airport which may save some time. There is also a saying that Lijiang is a place to hookup for young Chinese because pretty much the entire center of old town is a huge bar and clubbing area where the alcohol, holiday spirit and some sort of vibe seems to mark the visitors with a "what stays in Vegas" attitude.

Lijiang is beautiful and has lots of features. Waterways, stone bridges, old houses one both side of the cobble streets, red lanterns, temples, multi-level layers that seem to go on forever plus surrounded by mountains. Being a major tourist destination it's also trying hard to keep clean and tidy. The water system is helping there and the money pouring in keeps everyone busy to stay traditional as much as they can so you will definitely not find skyscrapers or even tall buildings anywhere near the city center (my visit has been years ago but I'm sure not much changed in the core area).

Overall I spent 3 days in Lijiang mainly because of my Lugu sidetrip so I would overall think 2 are enough if you just want to enjoy and soak up the town. It's become quite monetary about running bars in oldtown which is a negative aspect but you can still enjoy the town during the day and get a glimpse of the nightime before it gets loud and raunchy.