I feel like Burnout is sort of a "Desert Island" game. Or, if you could only afford one game, then BP would be a great buy. As is, I always feel compelled to play games that I can "finish" when I get some time. I've very much enjoyed the time I've spent on Paradise Island... But when I get an hour, and I can choose between finishing a game I've been playing, or tooling around in BP for a little bit... I almost never choose BP.
If Heavy Rain is too much like Indigo Prophecy (Farenheit) then I'd probably skip it. I know a lot of people love love loved Indigo Prophecy, and they were the most excited for Heavy Rain (loose sequel)... But I didn't really care for IP...