I lived in Dalian for nearly a year and thought it was a nice place to live. It's cleaner compared to the other cities in China, especially in Manchuria. It's also an attractive due to all the public squares. In addition, Dalian has a lot of tech start-up companies, and it's unofficially known as China's Silicon Valley.
Dalian is full of many very interesting stories. from its long occupation by the imperial Japanese for over 40 years to its proximity to Russia thus giving this very Chinese city a somewhat Russian fell to its importance as a major shipping port. Dalian is full of surprises. Throughout the city there are Japanese, Russian, traditional Chinese and modern western architecture. This visual stunner is not be out down by the many vast squares dotted throughout the city commemorating different important chapters of the city. Dalian today is fun, modern, and very progressive much like its many sister cities in China.
This is one of my favorite cities in China. I stayed here twice for school in 2007 and 2009, and visited with my wife in 2008. It is a decent-sized city but the people there don't seem as rushed or stressed-out as in places like Beijing or Shanghai; there's more of a laid-back attitude. Lots of greenery and well-designed public spaces thanks to Bo Xilai's beautification initiative when he was mayor. The air quality is better than in a lot of China, and the weather is pleasant during the summer and autumn. It still carries visible influence from its past as both a Japanese and a Russian port city, and its location means there's an active Korean community and lots of good Korean food. The local dialect is pretty close to standard Mandarin. Downsides? Its history is fairly recent and mostly revolves around shipping; if you spent a couple weeks doing intensive sightseeing you'd easily exhaust all the tourist attractions. It's not a big cultural center; it's big enough that there's a steady stream of stuff going on, but not the huge cultural smorgasbord of larger cities. The (English-speaking) expat community is pretty small. For that matter, English is not widely spoken among the locals. This is a plus if you're picking it as a place to go learn Chinese, less so if you're a foreign tourist. However, if you speak some Mandarin and are more interested in hanging out in a relaxed atmosphere than in sightseeing or an intense nightlife, it's a great choice.