I've only played Carbon (pc and wii,) ProStreet (wii) and Most Wanted (360.) I had undercover but traded it in because it was stuffty.
Honestly I like how they're putting you in one big race across the country (also first time using real locales i think) but some of the stuff like the storyline and cutscenes don't look to good.
I've played the first Hot Pursuit, Shift, Shift 2, and Most Wanted and they seemed to progressively get worse with the exception of one of the Shifts, don't remember which. The one giant race seems boring to me and the gameplay... looks, well, stupid to me as well. I don't think I'd like it. The storyline seems lame and the cutscenes cheesy.
Also Criterion should stop working on possibly stuffty NFS games and get another burnout title under way.
I agree, Burnout was always awesome. I haven't played much of Paradise but it seemed okay. Open world is something I never thought I'd see in Burnout. :o