Sisley is one of those brands where I just can't believe the cost is justified...they are EXTORTIONATELY expensive...if you can afford it and like them then go for it, but I think there are lots of good brands at lower price points! I love Liz Earle Superskin and that's much more affordable (though still not cheap).
I love them and used them when I was earning enough to do so. But they are extortionately priced. Have now 'traded down' to Clarins, which does suit me (personally unimpressed by Liz Earle on other hand). Have always had lots of compliments on my skin but really can't say hand on heart that it must be all down to the Sisley (and now Clarins) products. Genes, not being slim drinking lots of water may all have played a part too.Who knows?
Nevertheless still treat myself to a couple of Sisley products a year and would go back to using them all all the time like a shot if I could afford it!