I go to GZ at least 4 times per year and never have any problem. Just stay vigilant as you would in any foreign city. I never had any problem with taxi but I do speak Mandarin and fluent Cantonese.

Maybe its because its feels familiar to me, but I actually prefer GZ to Beijing and Shanghai.

As for romance, take the river cruise at night. There are a lot of companies near the dock. Costs around 150 RMB per person or so. Don't buy the ticket with the food, as the food is really substandard.

There is also an amusement park and animal safari in the suburb of Panyu which is about 30 min drive out of GZ. That's if your really looking for something to do.

Have fun!