I think that no game could catch up with TDU it's because, the latter in its time, offered something the others didn't, or offered in a way we haven't experienced before.
- Did we have open world games? Yes, every single NFS since UG2 was. Were they based situated in real locations? Not that I can remember (At least until FH came)
- Did we have street racing? Yes, pretty much every NFS since NFS1
- Did we have a big selection of luxury cars ? Yes, Gran Turismo and Forza
- Did all the cars had cockpits modelled? Not in Gran Turismo, afaik
- Could we change clothes, do missions, transport misterious packages, super models or exclusive cars? Nope, maybe in GTA.
And I could go on with many more, but as Lookie said, TDU actually let you feel like the car was yours and live like a rich guy who doesn't have to worry about money. You could go to the dealer, spec your car, choose rims, choose colors and drive off, straight to your house. And oh, the GPS in the infotainment system, I'm bored of reading "///M" or "AMG" or "Jaguar" or whatever it is, why can't we have this today? Okay, TDU didn't have digital tacho/speedo...
Well, they can call it... Test Drive "Unchained" or anything that suggests it's an open world racer :P