Linksys has revamped the user interface and slightly changed the feature set since the WRT54G's review. Since this review is likely to also be well-read, I've reprised most of it here - with appropriate text and screenshot changes - so that you don't have to click back and forth between this and the older review. The Performance sections are brand-new, however, so if you're already familiar with the WRT54G's feature set, you may want to skip right to there.
The WRT54GS (GS) comes in Linksys' pre-Cisco purple and grey plastic box. All indicator lights are on the front of the box and are bright and viewable from a wide angle. All network connection indicators have been scaled back to single Link/Activity types for the four 10/100 LAN ports, WLAN (wireless LAN) and 10/100 Internet (WAN) ports. Power and DMZ general indicators (Diag has been dropped) round out the blinky stuff.
The DMZ indicator now properly lights whenever the DMZ feature - which opens up all ports to one selected LAN machine - is enabled. The WLAN light is now also a much better indicator of wireless activity, briefly shutting off when the WLAN link is passing traffic. It also extinguishes when you set the Wireless Network Mode selector in the admin interface to Disabled to shut off the router's radio.
Four 10/100 LAN ports, one 10/100 WAN port and power jack are on the rear panel, along with the Reset switch, which now serves only a reset-to-factory-defaults function. Note that all ports are auto MDI / MDI-X (though Linksys doesn't spec or mention this) which means they'll figure out how to connect to whatever you plug into them, including switches if you decide to expand the number of ports.
Linksys didn't include the wall-mounting plate that came with my original WRT54G, instead now pagebreak
The GS uses a very different board design than its predecessor (Figure 1).
Figure 1: The WRT54GS board
The radio is now integrated onto the main board instead of using a separate mini-PCI radio. Linksys also tells me that it uses a different Broadcom chipset, that's needed to support the "Afterburner" capability. This means that WRT54G's can't be upgraded to be equivalent to the "GS". So if you want to play, you'll have to pay.
The radio is cabled to two RP-TNC style connectors (that Linksys uses throughout its 802.11b product line) which have two moveable, jointed dipole antennas attached.
Something that hasn't changed is that the GS is still based on Broadcom's BCM4702 Wireless Network Processor, supported by RAM, Flash memory, and an ADMtek 6996 for the 10/100 WAN Ethernet port and four 10/100 switched LAN ports.