Hi Jim,
Well, I'm sure you could have found most of the information yourself with G**gle but AFAIK:
- ATG has discontinued Dynamo Application Server in favor of IBM Websphere.
- JHTML, ATG's server-side scripting language has been deprecated in favor of
JSP - Their portal technology is not (yet) based on the Portal specification (JSR 168)
- Their portal framework is not compatible with
Struts (Websphere is).
- ATG being a small player on the market means there is a lack of
IDE integration (Borland, Eclipse, Netbeans, IDEA and others not not support it)
- Most classes in a web applications need to be on the global system classpath => i.e. redeployment of an application often means stop and restart the server
Hope this helps,