Two thoughts:
1. The SP2 firewall is still essentially protecting in-bound traffic. MS has expressed no interest in controlling outbound connections made by a workstation.
This is the fundamental argument for third-party firewalls anyway; the native ICF is actually a quite capable SPI firewall for most users, and the SP2 gives it more flexibility and ease of use. You can perfectly protect your system with ICF as shipped with XP, and it did nothing to prevent the growth of third-party products.
2. The delay, announced Wednesday, is for one month to allow the inclusion of a pop-up blocker, and handle some very specific hardware routers that showed VPN problems, and to test further the May SP2 RC2 bug reports and comments. The pop-up blocker was in the original plans, but dropped for various reasons in RC1 (beta testers did not like it in their releases). But Corporate clients wanted the feature very strongly. VPN has grown tremendously, and there are a lot of hardware/firmware specific quirks that need to be ironed out. That is being done now, announcements at WindowsHEC in May.
3. Lost in this firewall attention is a considerable amount of other changes to XP. These are the quiet changes to DLLs and APIs being used, to Group Policy, Control Panel applets, the entire Wireless suite, and other good things.
MS wants this to be right. There will be, just as after Service Pack 1, issues with some workstations.
But it seems silly to even imply a criticism for their efforts at this point.