Richard Monson-Haefel writes about alternatives to Ajax, and concludes:
There are today three leading platforms for developing Rich Internet Applications: Ajax, Adobe Flash Player (with Adobe Flex 2 or OpenLaszlo), and Java Plug-in (used with Java applets). None of these solutions are perfect – they all offer some advantage over the others. The fact that Ajax has ignited a renewed interest in making the Web a much better user experience is to be applauded, but don’t confuse the hype around the technology with the basic facts about the strengths and weakness of Ajax compared to its counterparts, Adobe Flex and the Java Plug-in. Ajax is good, but there is plenty of room for improvement.
Without a doubt Ajax is far from perfect. Personally, I think the acronym is stupid and the hype is totally undeserved. But the alternatives Richard mentions — Flash and Java Applets — lack one crucial feature IMO: A decent fallback strategy. My personal favorite is plain HTML, with optional Ajax goodness added later on.