A cheap 100Mb/s router uses a switch that runs at that same speed. That sounds fine, until you think about how a switch functions: it reads a block of data at 100Mb/s from one port, and then writes it at that same speed to a different port. Net throughput: 50Mb/s. (And some very cheap ones can't even do that.)
A better switch has a bigger buffer, and can read at the same time as it can write. That gives it a throughput of up to 100Mb/s, for a single connection. If two people use it at the same time, or you're talking to two different devices, that bandwidth is shared.
802.11n runs at a speed of up to 300Mb/s in the best case, but the encryption uses up half of it, and that is one-way, so it's actually 75-150Mb/s max, for all connections shared. But you need a switch that has a throughput of at least 300Mb/s to reach that.
So, you want at least a real Gigabit switch in the router, and at least 3 antenna's on it.
But, if a router or switch says it's "Gigabit", that only means that it can read and write packets at that speed, it says nothing about the bandwidth at which it does so.
Just about all consumer routers use a microcontroller to do all the work, and so the actual throughput of a Gigabit router depends solely on the speed at which that microcontroller can read and write the data. And I've yet to see a router that states on the box what microcontroller is inside, and what that sustained throughput is.
Further, the WAN (ISP) connection is much more complex than the LAN ones, and many routers are still designed with a maximum WAN speed of 10Mb/s in mind.
So, if you want a good router, you have to find out what the sustained switching throughput is, as well as the WAN throughput. (Or, in other words, if it has a fast and expensive microcontroller.)
And in that, the D-Link DIR-655 outperforms most routers that are twice as expensive. It's (next to some of it's more expensive siblings) one of the fastest routers available in the consumer market.
It's like the original WRT54G, which was also quite overpowered when it was introduced.