My two cents on H&M quality and sizing:
tops: The quality of the thicker t-shirts and the ones from the L.O.G.G. line and especially of the men's line is fine. Everything is else is crap! I've had so many tanks shrink from covering my butt to baring my midriff after one wash
They're often itchy and uncomfy, too. Sizing is all over the place, I think I've had everything from EU32 to EU40 fit me pretty much the same, haha.
jeans: I've only bought one pair of jeans from H&M so far and that's because they stretch so much when wearing them, they sag in the butt and I hate it. IMO the jeans run very big compared to traditional designer sizing but similar to American brands. And I've never seen anything smaller than a sz25 in my H&M, I think.
Blazers and cardis never fit me, way too big around the waist and too tight in the bust and armpits. Arm sleeves are often too short on me. I've had some cardis before (can't resist their cardigan promos) but they all got holes around the seams and on the arm sleeves, unfortunately.
accessories: cheap and cheerful B)
underwear: I love H&M bras. They fit great but I wish they did more unpadded ones. I really hate push-up bras and even when taking out the pads they still make your boobs look kind of fake, haha. Not a big fan of the panties and thongs because the cheap fabrics can get itchy
I've kind of sworn off H&M lately, haven't bought anything there in a while. I get all my basics from a brand called American Vintage. A bit pricier than H&M and AA, but easily to be found in sales and outlets and the quality is amazing.