I have lived in Gloucester for 2 years, previously lived in Cheltenham for 2, and prior to that lived in Devon from birth.
I moved here because of jobs - that is the best thing abouyt the area, there is a lot of work here for my industry (aerospace) and is easily commutable distance also from Bristol, Birmingham etc.
But...I would rather not live here. I don't like it at all. It is the worst of both worlds - is a city so has all the disadvantages, but is only a small city (more a town really) so is parochial and small minded. As soon as dd is 18 and has left home I am moving away.
There is a large amount of poverty in Gloucester, which is evident. Property is rather expensive - I used to live in a 2 bed flat in Cheltenham, howeer you can buty a 3 bed house in Gloucester for the same money. People in Cheltenham are very snobby towards those who live in Gloucester. Personally I don't think Cheltenham is any better, yes it is pretty but is still just a small town. Lots of stuff going on, lots of festivals, but it still isn't as dynamic as (say) Bristol or Bath. A very small town feel to it.
Re flooding - our house in Gloucester was submerged in 6 foot of water in 2007! Uninhabitable for a year. However SO many places in Gloucester flooded that year that have never seen flood water before, our house was one. There was an enquiry and it was proven that Severn Trent water had blocked drainage culverts which had not been maintained, which meant that the deluge could not run off, and hence the flooded houses. Our house was categorised flood risk 3 initially (what fun those insurance payments were) but had been downgraded to risk 1 (which is the lowest risk) in light of that information. However there are places which are a risky flood plain as other posters have suggested.
I don't want to run down Gloucester, I think it has a lot of potential, however with Cheltenham next door it is not likely to get the attention it needs. The city centre is rather ugly, it has a look of a city which was bombed in the war (it wasn't), all concrete 60s madness. But the cathedral green is beautiful, and there are a load of older tudor buildings. But it has an air of somewhere neglected.
There are very few restaurants, there are very nice pubs in Painswick and Cranham, but for restaurants/nightlife you will need to go to Cheltenham tbh.
That said, people from Gloucester are incredibly friendly, they are like Bristolians, very chatty and down to earth. The accent is rather funny (think Bristol with a twang) and my daughter is the proud owner of a full on Gloucestershire burr!
Also (I will shit up soon) if you have a child of late primarty age, Gloucester operates a compulsory 11+.