As an Ikelite user, this is what I notice when I'm using my rig next to others with a Subal/Aquatica/Sea&Sea/etc.
- The Ike is bigger. Not as much as you would think, but yes slightly larger. I had mine sitting next to an Aquatica on the camera table and it's just a bit larger.
- The Ike is heavier. This is true. The aluminum Aquatica I was comparing it to seemed much lighter when I picked it up. Of course, whereas my Ike is just slightly negative by itself without strobes, the Aquatica is more negative in the water. Not a big deal for either one, but just something to know if you like to one-hand shoot like I do. I believe an aluminum housing will require more buoyancy aids than an Ike. Well, unless you have HUGE arms 
- The Ike is easier to get a verifiable seal. Being able to see the o-ring seal AND you can tip it over to the side and very easily see if there is any water seepage into the housing.
- People say Ike makes it hard to change battery and memory card. Not any more. On my Ike-housed D70, I did have to take the camera off the housing back mount to change either one, they fixed this on their D300 implementation and you can leave the camera attached. However, there can be other issues with pulling a camera in and out of the housing (see next bullet).
- People say Ike's are complicated when mounting lenses. This is true for any zoom lens on the Ike housing. You have to put the camera into the housing from the back, then put the zoom ring into the front of the housing with the port off and then mount the port. Most aluminum housings mount the zoom ring to the lens and can be inserted from the back of the housing making for an easier ingress/egress. Is this a huge deal? Not really, I can change lenses and ports in just a couple of minutes. And if it's the macro 60 or 105 lens you don't have any zoom ring at all, so it's quick.
- People say Ike's port mount is inferior. Quite frankly, I never liked Ike's two-point port mount. It never failed me or caused a problem, but it just seemed "flimsy" in comparison to the locking bayonet or screw mount on most other housings (screw mounts have their own issues however). But since I had Ike upgrade my housing with the new 4 lock port mount, it's VERY solid and quick and easy.
So, net result, I will keep my Ike because it's actually very easy to use and maintain. It's very easy to handle underwater. With two DS-125's, it is dead simple to adjust strobe power with one knob on the back of the housing for two strobes. If you only dive maybe two weeks per year like me, this is a great solution considering the Ike housing was $1425 vs. an Aquatica at $2700, Sea&sea at $3500 and a Subal at I-don't-want-to-know. Saving $1300 means another scuba trip for me and that's worth it. Oh and that's just for the housing BTW -- ports for the other brands are about twice the price of Ike ports.
If I had the bucks would I buy an aluminum housing instead? You bet, but being a land-locked amateur it's just too expensive for the minimal benefits I would receive. There is a certain "cachet" to owning an Aluminum housing and if that kind of thing is important to you, sort of like owning a BMW instead of a Subaru WRX, then by all means, go aluminum. I really only care about the photos.
OH and there is one additional benefit to buying an Ike. I don't have to figure out whether to say Al- Loom - I - Num vs. Al - U - Min- I -Um. My apologies to our British Friends.
Just my two cents. What's really important is knowing your gear intimately so you are not fumbling around with it when that Whale Shark comes by with a mermaid riding it 