I love Decathalon, as much for its chaos as finding what I want. I have used them for some years though so understand their foibles. Perhaps their being French has something to do with it? I am blessed with 3 within 30 miles here in Brum and they vary considerably in quality of store with Giltbrook in Nottm being the best.
Capt. P's comments are all solid and true - I bought a windstopper jacket from them, but prior research on their website in the hiking / camping category failed to highlight it. Having bought it I entered the details in their web search box and found it in their Ski section because the colour was Ski red!!!
As far as their quality, overall really impressed although their sizing is all over the place and you can spend more time trying different sizes on than looking at different items. Actually prefer them to GoOut where due to it being major brands you really do need to have done your price research beforehand to get a decent bargain