Its a bit scary to run an update option on a stack and potentially have all your running instances destroyed and replaced - would be good to have a dry run option
It would be very useful if you could query values from resources of other stacks, or potentially arbitrary resources from the account based on tag / resource type / other metadata.
You have to wait for the whole stack to finish before outputs are shown - a major use of outputs is showing ip addressses of created instances - it would be good to show these immediately when the instance is created if the output references no other resources.
Link to resources within aws console
AvailabilityZones and VPCZoneIdentifier should not both need to specified.
Its not clear from the docs whether an input of this type can be used directly as an array - eg for passing a list of subnets of an ELB. The docs show an example of using the Fn::Select function, which implies this is the case, but it is not clear without doing a test.