As you might expect from a vibrant city, the transportation in Osaka is excellent. Although the subways can get very crowded in rush hour the services are frequent and delays are rare. So rare, in fact, that telling your boss you were late for work because the train was late is not a valid excuse. In the event of any delays commuters are given little notes to prove it.
There are plenty of buses too but long journeys can be expensive. The train is Osaka's preferred method of transportation.
Osaka has excellent connections with the rest of the country by rail, with Tokyo two and a half hours away on the bullet train and Kyoto about 30 minutes.
It also has a first class international airport and busy port, with ferries departing to various destinations all over Japan, and further afield.
Although the city is active at night, trains aren't. They generally stop around midnight and metered taxis are quite expensive. If you're thinking of having a late night then getting the morning train home at around 5am could be your best option.
Osaka is famous for some of Japan's most iconic food like Okonomiyaki (known as the Japanese equivalent of pizza) and Takoyaki (balls of fried octopus in batter, served on street stalls) and is known as the culinary capital of Japan. This is largely due to its merchant history as old Japan's main port for the import of various ingredients.
In addition to all its restaurants, Osaka is also home to the longest covered shopping arcade in Japan, an area selling electronics to rival Tokyo's Akihabara, a large aquarium and Universal Studios Japan.
The city is in competition with Tokyo, as a conversation with any proud Osaka native might show you, so it isn't lacking any shopping or entertainment opportunities. It's known for its comedians and you can find performances of some of Japan's traditional performing arts while living in Osaka. The locals like their sports, with Kyocera Dome being home to two baseball teams, Orix Buffaloes and Hanshin Tigers, who are known around Japan for their passionate fan base. There are also two soccer clubs.
While it certainly has an impressive skyline, Osaka isn't exactly a “beautiful” city. By Japanese standards it's fairly noisy and grimy and has little in the way of traditional sites other than the famous Osaka Castle.
However Kyoto, with its array of World Heritage shrines, temples and gardens, is just a short train ride away. At a similar distance are Nara and Kobe, a cleaner and more modern city that was completely rebuilt following an earthquake in 1995.
Osaka has the highest crime rate in Japan, but it still compares favorably to large cities elsewhere. Japan is a very safe place and it's unlikely you would have any trouble walking alone at night.
As an expat you're more likely to be approached and have someone try to practice their English on you than anything else. That being said, you should take the same precautions you'd take in any other big city, just to be sure.