That's a tough question. I have read a lot of case reviews, main difference is that Lian Li uses 99-100% brushed, anodized aluminum as the material.
This is expensive, lightweight and very slick-looking. Antec/Coolermaster etc. use the same material but typically not for every part of the case.
Also Lian Li focuses exclusively on case design and manufacture, as a result they have often been the first to innovate stuff like cases with heat zones, vibration-proof HDD cages, sound-dampening pads on sides of case, etc.
Lian Li cases are often just better designed, also they have a very spare, minimalist aesthetic style that many people happen to like. They never have "pimped out" cases with lots of LEDs, flashy designs and transparent windows. Lian Li cases are elegant and artistic.
More mature if you will. The difference between a stately Rolls and some 20-year-old kid who has to have glowing lights under his heavily modded Civic and those rims that never stop spinning.
I don't deny Lian Li cases are overpriced. They sure are, and this one was particularly outrageous, with an initial street price of like $380, before shipping costs.