London is a big crowded city. Wales is very hilly so the people are more spread out. And the cost of living tends to be cheaper because London is more expensive than anywhere else, being the capital of the UK. Friendliness is also a function of "how big" - people tend to be more friendly in smaller places, and that's true pretty much everywhere.
Laws are exactly the same. English law applies in Wales, and has done since Henry VIII annexed Wales around 480 years ago.
The Welsh accent is extremely distinctive. It's very "sing-songy" like Swedish, and quite unlike anything else, though quite easy to understand. This comes from the fact that there is a Welsh language, very unrelated to English, and if a Welsh speaker speaks English, they'll naturally have that accent in English. Not surprisingly, everyone else from Wales sounds like that too even if they don't know any Welsh - only 10-20% of the Welsh population know it at all well. However, you will see Welsh all over the place because all public signs are required to be bilingual.
And you can hear it on TV, particularly on Channel 4, which is called S4C (Sianel Pedwar Cymru) in Wales. One small mystery is why the apparent number of people who watch the soap opera "Pobol y Cwm" is more than can possibly understand it - are they all trying to learn Welsh and watching it for practice?
Do not attempt to say any words in Welsh unless someone has shown you how first. The alphabet works very differently from how it does in English and you WILL get it wrong. For example, the familiar Welcome to Wales sign, "Croeso i Gymru", is pronounced "kroy-so ee gum-ree". You may notice words that appear to have no vowels in them, but once you realise that w and y are vowels in Welsh, they'll look more sensible.
The weather tends to be wetter in Wales. British weather is dominated by an endless series of depressions (low pressure areas) coming in from the Atlantic, those bring rain, and naturally they'll drop a lot of the water on the west of the British Isles first.
There are a few regional foods, and Wales is famous for lamb, but otherwise food is the same as the rest of the UK. And that's all the differences worth remarking on.