Again, most cheap air ticket to Europe are sold by the three Middle-East airlines. Qatar usually fits our schedule well because it offered a midnight flight to Doha (like 0:00 in HK) and arrvied at Europe in the afternoon of the same day. So we can finish our day of work, go home and wash up, have our dinner and start our trip.
My last trip to Italy also went via Doha and I had mentioned that there were 3 landmarks in Doha airport. Last time I got 2 and this time, with 3 hour transit time, I went to take pictures of all 3. Here is the third one. We also rode the overhead rail and walked around the shops.
BTW, if you have more than 5 hour transit time, you may apply to have a short city tour in Doha, offered by Qatar airline. They will take you out the airport and bring you back before your flight time. Last year this trip was free of charge but it seems that you have to pay some money for the tour now.