I lived here for 7 years and consider it my second home. I rate it 5 stars as I love the city! And yet I would completely understand if someone hated it. It is a beautiful mess of a place.
For work, I love the buzzing entrepreneurial energy. You get the feeling that everything is possible with the local young population's enthusiasm and talent.
For play, the food is just amazing. Vietnamese cuisine is of course great by itself, but in this megacity the selection is out of this world. I recommend going to Vietnamese barbecue restaurants like 5ku. And having the best phở (noodle soup) you will ever have at Phở Hòa. I also never miss a chance to eat Vietnamese beef steak at Bò Né Lệ Hồng. I often eat on the streets or in the lively alleys, where I tend to go for bún thịt nướng (rice noodles and grilled pork), cơm tấm sườn ốp la (broken rice with a pork chop and an egg sunny side up), or a bánh mì (filled baguette) of some kind. I could go on...
Go any time of the year, even the rain season is nice most days. Stay in District 1 or 3. Avoid the backpacker area like the plague.
The main weak points are the traffic and the polluted air, so be prepared for that. Use Vinasun Taxi, Mai Linh Taxi, Vinataxi, or Grab to get around when it is too far to walk.
I tend to recommend combining Ho Chi Minh City and the island Phu Quoc. You then get to enjoy the best of two worlds, this energetic place, and then an ice-cold lemonade made from local lime fruits under a palm tree on the beach.