First depending on the router it might be worth a look towards hacking it. Most ISP provided boxes are not locked down that well.
Secondly even if you can not hack it then you can almost always stick DSL modem if the ISP will send that (your ISP will usually sell a DSL modem for pocket change if not) and use the old router for everything else (wireless, wired and security). Only real note there is set one or the other to do DCHP or you will end up in a mess.
Wireless N- I will note that even in Canada speeds are probably only high enough to challenge wireless B let alone G and especially N. Similarly wireless N is fairly new (although it is not quite an official standard yet I doubt it will change) and will require changing network cards.
If you have internal networks then I say suck it up and run cable or use ethernet over powerline. Wireless is fine for surfing on the chair but I reckon anything that requires speeds like those N provides will not be fun when it drops out (looking at media streaming and gaming).
Back on topic for a home router there is not much that is truly necessary, some of the really cheap ones dislike torrents if you have connections set up in the hundreds (often a bad idea even on commercial/enterprise grade hardware, regular windows/SMB file sharing is just bandwidth rather than connections). I guess it remains to be asked what do you want to do
If you want to run a server then things change (port forwarding comes into play), available on just about everything but gets nicer the higher up you go.
If you want hardware firewalls and do not want to run a PC to do the job then that is another thing. Again basic functionality should exist in most things but if you want really nice stuff here you are going to need to spend a bit.
As a halfway house between firewalls and forwarding is highly configurable security- this is something special as some of the really nice stuff will allow highly tuned security (filter by mac, name and select how fast you want it to run) and other such things (QOS- you can tell your games to be looked at first over an email lookup).
Printer sharing is an odd one and I will ask you what you mean by it:
Easiest way is probably just to share it on a computer using SMB (right click- share printer) and go that way.
Some printers will be able to share themselves (usually higher end laser printers- your basic combo printer scanner you scored for $50 + cartridges less so) which is only a matter of a network port.
After this you have router level stuff (if you want to stick it in the USB port a router might have), most routers run on linux at some level and so will be limited somewhat here (cups is great if you have something that works but if not then yeah)- this is a minefield and I do not wish to call it without more info.
