You have the 2 department stores next door to one another - Printemps et Galeries Lafayette.
I always used to be a Printemps girl and then some years back they overhauled it into a very upmarket store and I feel more confortable with Galeries Lafayette
Both of them have roof top terraces where you get great views other Paris. They also both have some nice architecture-Printemps is the prettiest and they have a stunning cupola above the top floor restaurant and Galeries Lafayette have an amazing dome and an around balcony on every floor so you can look over the whole centre part.
Printemps is designer, designer, designer. GL is designer but with boutique shops and highstreet (Zara, Promod, Mango) as well
Both of them have very well stock beauty counters and the kitchenware/household/linens has to be seen to be believed
No idea how they compare to London dept stores as I haven't been in years
Oh and if you go to guest services show your passeport you used to be able to get a card for -10% and a gift. My mum has a fair collection of bags,scarfs and notebooks from over the years
Galeries Lafayette also have a Gourmet food store with allsorts of things that can make nice foody gifts as well as nice picnics