While it is true that the WRT54GL was _the_ goto firewall router for the 2000s, it is too slow to handle today’s high speed broadband connections (Comcast now routinely bursts at 50mbit/s even on a Starter 12 mbit/s plan.) Also doesn’t offer 802.11n or 802.11ac WiFi, which is needed for 1080p.
I upgraded to the TP-LINK WDR4300 because it has all the needed specs for a good price: 128MB mem, a fast ARM SoC, USB for JFFS storage, dual-band antennas, and best of all flashable to OpenWRT.
I just run the OEM software package, haven't tried OpenWRT.
In my experience the WRT54GL is just as good as a wireless N router in the consumer price range. Despite the claims, wireless N degrades to 72 Mbps over about twenty feet of air. It's not unusual for me to see the signal of my G network one floor away running at 54 Mbps -- the same speed as all three of my N networks at that distance.
So I would say for most consumer applications WRT54GL will be just fine, and if he needs more, either bring the coax right in next to the TV and hardwire the TV to the router with Cat-5e/6, [and/]or buy an 802.11ac router. I've never really seen much difference between G and N, and in fact have found G to be more reliable when the signal forces speed within the G rated range.