I have an Ike housing for my D200 and I love it. I also had one for my D100, and I loved that one too. I have 6" ports, the 8" dome, and DS200 substrobes.
The price is good, the quality is fantastic, the customer service is superb.
You will never find a definitive answer as to why you should or should not buy Ikelite.
There will always be people claiming the quality isn't there, that their aluminum housing is rated to 300 feet, and Ike housings are only rated to 200 feet. How often do you dive beyond 200 feet?
There are plenty of folks who point out that the Ikelite housing is HUGE! Put an 8" dome and a couple of strobes on their housing. It's just as big. Sure, the housing could be 1/2" narrower. How will that make my photography better?
The Ikelite housing gives you TTL for $1500. With the other housings, TTL may not even be an option, and if it is, tack $500 onto the $5K price of the housing.
It's a simple question -- how much do you want to spend, how much value do you want for your money, and how do you perceive value?
I would not hesitate to recommend Ikelite to anyone.