I have the Size 29 Biocube (it actually only holds about 23 gallons) and I love it! This is my first sw tank, so I don't really have anything to compare to, but I do like the fact that since everything is included to get a good tank up and running, I can concentrate on on the aesthetic aspects of the tank (I love decorating!) and not have to worry about putting together the right combination of pumps, skimmers, lighting, etc. I'll have time to worry about all that stuff when I go to plan my next (and much larger!) tank.
I'm still in the early stages of setting up (I have LR, sand, snails, and algae), but I'm excited about the possibility of having something that half as nice looking as some of the beaut's seen on this site!