Tldr; If you got on fine in London then you'll get on fine in Dublin.
I am a web-developer from Cape Town, South Africa and have been living in Ireland for 11 years, the last 5 in Killester in Dublin. I am mid-30s, my partner is Irish, and we have 2 young children so my perspective of Dublin is shaped by this. I lived in London for a few months in my early twenties and visited it regularly.
There is a good tech community in Dublin and plenty of jobs. It is smaller than London and you will get to meet and know the community quite well. The leaders are accessible and very giving. There are overlapping meetups every evening of the week across all areas of tech. Google, Facebook, AirBnB, and many other multi-national tech firms have their EMEA HQ here and they get involved in the local tech community. It is an alcohol centred culture though so events are often in pubs or have free beer.
The Irish culture is friendly and robust which also means you can't be thin skinned. Having an Irish friend, not acquaintance, already helps a lot. I had two children with one which really opens doors into the heart of Irish culture. Without it you will find the Irish friendly up to a point and then you are unintentionally excluded. This is purely related to personal relationships. Business relationships are very open here and there are many multi-cultural partnerships.
Being from South Africa I find the diversity lacking but at the same time there is a good percentage from outside of Ireland. Italian, Portuguese, Chinese, Indian, Pakistani, Syrian, Iranian, English, Polish, Scottish, Welsh, Croatian, Spanish, Lithuanian, Estonian, Ukrainian, Brazilian, Canadians, and people from the USA amongst other nationalities. Caucasians do dominate though. Gender diversity is still a challenge. The LGBTQA community has improved dramatically especially with the passing of same-sex marriage in recent years. It's not perfect but it is better than many other cities.
There is a housing and office shortage though which means rents are high in the Dublin county. Though London is still more expensive even with BREXIT. I pay €1475 a month for a 3 bed town house near the DART (commuter rail) which gives me 10 minute access to the city centre. I would highly recommend living near the DART.
I would recommend Dublin over London personally. The size is Goldilocks, just right, the tech community is booming, you have easy access to London and the rest of Europe as well as North America. A short walk and you are at the beach, a 30 minute drive and you are in the countryside. There are festivals, conferences, film, music, and art events, international tech leaders visit often, and the Guinness is good.