This place is really cool and I don't think I can add much more than what other yelpers have said but I like the uniqueness of this mall. Each "lane" you walk down on has a street name so you can remember where your favourite store (or shack) is at and although I've never been to HK, I'm sure it resembles the street markets!
Gwai-loh's and non-asians need to beware, I've heard of many times the store owners jacking up prices when they see non-asians enter their store. Make sure you go with a chinese friend and it'll be all good!
Also I don't think any story about Pacific Mall is complete without this: http://www.youtube.com/watch?v=jsd0ZJOrIZQ (starts at about 25 seconds in)