I find the shops to be worth it. I have been very happy with the selection, but movies we consider to be popular and big in the west may not be the same movies they consider particularly popular here.
Region 3's are cheap, Region 1's are expensive. It's an import issue - why import Region 3's? Don't bother with the region codes - as almost all VCD/DVD players can play all regions.
I have had no problem with the legitimate VCDs or DVDs I have bought, except for maybe the darn plastic wrapping.
DVDs are typically about 50% more expensive, but still at a very good rate. But be prepared to spend time looking through the English section collection - real gems are to be found, but in between are English movies you may never have heard about, or haven't heard about in a long time, interspersed with last year's hit.
I don't find HMV's collection anything special, except for their higher prices and comfortable elbow room while you're searching. There is an added benefit with making special orders, but don't go there unless you like to spend too much money in western shops like most expats.