I have used the Ikelite housing for a compact. I have a metal housing (Nauticam) with a cropped sensor DSLR (Nikon D7000).
The Ikelite housings are well made and economical. However, they are essentially boxes. Being a box, the system is pretty bulky. Ikelite makes the controls work over a bit of distance to the camera body. The distance the controls operate over makes for a less than precise control of the camera. Now my metal housing is custom made for its particular camera body which means it fits much more closely to the camera making it more durable and more compact. All of this comes at a price. I think Ikelite housings come for something like $1,500 and metal housings start at the low $3,000. Now you will probably have strobes, ports, gears and so on. So the overall difference in price between an Ikelite system and a metal system may not be as great as one would think. But you still will pay about $2,000 more. It is your call on whether you think it is worth it.
The major drawback on a DSLR vs a compact (besides the price) is the size and weight of the system. My compact was pretty easy to pack away. The DSLR system with all it ports, strobes, housing, lenses, bodies and so on comes to nearly as much as my dive gear. Underwater it is much larger to handle but not that bad.
About the clarity of above water, not really. Underwater photography is a whole different world than surface photography. There are a number of issues to deal with. First off, you go down about 15' and there are no longer any reds. Longer wavelengths of light are absorbed in the water column. So if you want the natural colors, you have to bring your own lighting source down with you like strobes. I have taken shots of fish against what I thought were drab backgrounds. When I looked at the photos, what looked like greys and muddy browns were actually garish oranges. So if you want real color, your maximum shooting range is something like 5'.
Also, water has stuff suspended in it. If you want nice crisp photos, the closer you get the better. Again, long range is about 5'. So you either want to have really wide angle lenses. That is why the Tokina 10-17 lens is so very popular for cropped sensor cameras. You can shoot a photo of a diver from really close and get them in. It is not such an issue with macro photography because you are close by definition.
You might want to get The Underwater Photographyer by Martin Edge. It is a superb book. Reading it will give you a decent start on the challenges of underwater photography. Sure the book costs something but it is cheap compared to the money for a DSLR underwater system.
After using a range of underwater compacts with less than desirable results I would like to get my Canon 600D under the water to get some shots. I have heard good reviews about the ikelite housings however I am wondering whether the camera will produce the same speed and clarity I get from it above water? I would like to add a strobe as well as I realise this will make a big difference. 
