Hola! :)
I was in a very similar situation to yourself almost 5 years ago so I'll try and list some of my thoughts and experiences.
I was working as a backend developer in the UK, my girlfriend was off doing her masters and told me I should do something interesting with myself as I felt stagnant in the job I had at the time.
I'd always loved Spain and Catalunya so took the plunge to move out here, my girlfriend joined me and we've now spent almost 5 happy years about here in Barcelona.
Getting a job:
- I found interviews to be similar to interviews in the UK.
- Companies are much slower in getting back to you and moving you through their pipelines. One company came back to me 3 months after having offered me a job and wondering why I'd had to look for other options.
Working/Work environment:
- I joined a company of around 60 people, don't fool yourself that the work environment will be in English just because the interview was. I personally wanted to learn Spanish but it was still much tougher starting a job, a new life and a new language(s).
- While quality of life is better I'd say the work environment is tougher, people work hard and long hours here, at neither company I worked at did we do a standard 9-5. 9-7 was much more common with an hour for lunch.
- Management feels quite old school, they can be more rigid and traditional than say in the UK. Developers on the other hand feel ahead of the curve, there is more interest in side projects, new tech and trying out different skills.
- Salary is quite a lot lower, I took a 30% pay cut when I moved. I managed to get a couple of pay raises but the ceiling and cadence of raises is much lower. I'd attribute that to the more traditional management treating workers as equal resources and also that back then there were a lot of talented developers around (and less larger companies like King were in the area).
- Both companies I worked at worked in English official but in reality it was mainly Spanish, switching to English if there were non Spanish speakers present. I'd say having fluency is a huge huge boost to your career potential (and ability to make friends) :).
Quality of life:
Quality of life is great, a slower more family focused culture and a plethora of fun things to do within the city and surrounding areas. It really makes such a difference having nicer weather for both your mood but also ability to get out and do more sport or taking long Sunday walks (a great pastime here).
I think most people responding to you will rave about the quality of life (I'm one of them) but let me gave you some things that are tougher.
- If you want to learn and live in Spanish then you are best off in Madrid. Significantly less tourists and the use of just Spanish means immersion will be much quicker. Barcelona is great but due to having two official languages, a ton of tourists and foreigners means that a lot of people will fall into just speaking their native language anyway. You really need to make an effort to take classes, not switch to English and persevere. As my partner is also British we've had to make an extra effort as we speak English with each other.
- Making local friends is quite tough, all our friend are Spanish speakers from outside of Catalunya or South America. Locals are very friendly but they tend to have grown up with their friendship groups and it can be harder to integrate (doubly so as their are two languages and learning both to a good standard is tricky).
- Do not live anywhere near the center in Barcelona, tourists invade the city and really make it quite unpleasant. House prices are also rocketing for renting at the moment.
I now work remotely for a US company as it seems the best of both worlds, I love living here, the people,culture,food and weather all combine to make me happier. If you are serious about taking the plunge I'd look ASAP for a Spanish teacher, it'll be the best investment you'll make! Best of luck!