Athlon64 was a fantastic processor, and it really crushed P4 in terms of features and performance, and of course it helped that P4 was rubbish from the start, The early P4's were a considerable 'downgrade' compared to high end P3's.
AMD got a lucky break, and a taste of holding the performance crown. But will they get it back... Who knows, but Phenom isnt looking great. AMD really needed a chip which was faster than Core 2 "clock for clock". Phenom only matches performance, and when ramping up the clocks it seems to make Prescott look 'good' in power usage!
Sure it may improve when AMD get a 45nm process, but Intel will release their improve Core 2 processor Q1 2008, and thats the chip that Phenom will have to compete with. By the end of 2008 intel will release its next architecture, Intel lost quite a bit of respect during the P4 era, and it seems the top dogs at intel want to ensure they have world beating performance for the forseeable future.