I'm on my third bottle with this cleanser.
I purchased this at the Dermalogica counter about a year ago because it was marketed as a gentle cleanser. While my skin can be quite oily in the summer, it tends to be drier in the winter. Plus I'm acne-prone, so I need something that cleanses gently, yet effectively.
I think that the Special Cleansing Gel covers this. A little goes a long way, so one bottle, while expensive, will easily last you 3-4 months. If you cleanse twice, it can be a little drying, so this is something to bear in mind.
I wouldn't say that it does anything special: it cleanses well, it doesn't dry out my skin, it doesn't cause acne and it doesn't doesn't have overpowering fragrance. I don't think that it warrants its price tag, to be honest, but it's really challenging to find a good cleanser that effectively does the above.
One last thing to note. It looks like Dermalogica have changed the ingredients (at least in the UK), so I have copied out the list below as seen on their website (https://www.dermalogica.co.uk/special-cleansing-gel/3,en_GB,pd.html):
Water/Aqua/Eau, Disodium Laureth Sulfosuccinate, Sodium Lauroyl Sarcosinate, Quillaja Saponaria Bark Extract Lavandula Angustifolia (Lavender) Oil, Melissa Officinalis Leaf Extract, Citrus Limon (Lemon) Peel Oil, Citrus Aurantium Bergamia (Bergamot) Fruit Oil, Cymbopogon Winterianus Herb Oil, Glycerin, Cocamidopropyl Betaine, Coco-Betaine, Hydroxyethylcellulose, Sodium Cocoyl Isethionate, Capryloyl Glycine, Sodium Lauryl Sulfoacetate, Methylpropanediol, Ethylhexylglycerin, Caprylhydroxamic Acid, PPG-5-Ceteth-20, Sodium Hydroxide, Disodium EDTA