Dhoom 1 was the best. It had a good story. If it wasn't good, we wouldn't have had a Dhoom 2 or a Dhoom 3 either.
Dhoom 2 had Aish as Su-nai-na. Urghhh! But I really loved the scene where Hrithik is disguised as the statue in the musuem. Otherwise it was bleh!
Dhoom 3 was shit. I'm only okay with this coz I didn't waste my money on these tickets. But I feel sorry for all those who went to theatres to watch it.
So yes, Dhoom 3 was a success only because it was a part of a big franchise and people think Aamir is some superintellectual God of movies and rush to watch his movie. If Aamir would have done this movie in 2004, Tingu biker wouldn't have collected even 20 crores.