Wasn't the Rover V8 designed by some American chap? And then Rover bought the design...?
Anyway, a few things from my perspective:
1) Rover were completely outdated in terms of their workforce and applied engineering (not saying their designers were rubbish, but they were only allowed to be very conservative). I can remember a news article when BMW took over Rover where a line worker was shipped over to Bavaria to learn how to work properly... he was completely dumstruck by the workers at BMW and simply couldn't comprehend how they worked so hard in the time they did.
2) Their cars - I've been in numerous Rovers and not really been impressed by any of them. A Rover 75 I was recently sat it had some even worse plastics than my VW Polo... which cost a helluva load less. And the 75 was engineered by BMW.
3) Desperation: their MG-Z or whatever that uber, Mustang-engined coupe was called could have been awesome... had it been designed and engineered by somebody else. As numerous journalists have explained, neither it's performance nor its quality matched other coupes in the same price range. Rover needed money quickly.
4) Their owners: inbred inefficiency cripple the company. You see it in the NHS, the various national transport networks, the civil services, etc. Funnily enough, all of them are or were nationalised at some point and then been run by people who really didn't know what they were doing. As such, workers could get away with pretty much anything on the production line.
5) The ****ty Rover. Please. Anybody that imports a car from India, slaps a Rover badge on it and expects it to sell is desperate beyond imagination.
I would say that Rover has never built decent cars because I know they have. I won't say that all Rovers are rubbish because I'm sure they aren't. But will I ever buy one? Hell, no.