I am generally impressed with the quality in Uniqlo, I would say you get value for money. However, I don't generally expect them to last years and years because I think of them as basics that I will wear a lot in a season and then I don't mind discarding.
I bought a lot of heattech tops last year which I still wear this year, a few are looking slightly bobbled this year but since I mainly wear them under either items this is not a big deal for me. I find they keep me warm rather than make me sweaty.
I like Uniqlo for basics - T shirts generally good, heattech tops very cosy and quite thin so good for layering. I also have one pair of boyfriend jeans which are in thier 3rd year and still get admired.
The jeans are great. I think they are every bit as good quality as Gap or similar and half the price. They have really nice coats and jackets this year. Also agree with heattech - lovely vests, T-shirts and longer sleeved tops for layering in loads of colours.
They often do deals on the jeans, too, so watch out for those. I got two pairs of really nice straight leg slim-cut jeans for £25 last year. Even if they hadn't lasted, I think that would have been worth it, but they are still going strong this year.
Also, there are lots of good cotton jersey basics at very good prices.
I love Uniqlo and think the quality is great for what you pay. My best buys have been their trouser style leggings (£15 last year, still going strong and fitting well under my 5 month pregnant bump) and a long modal cotton cardigan/blazer which has washed amazingly well, no bobbling or loss of shape at all despite being worn a lot.