First of all, Taxes are higher with no personal allowance.
Not true. When you start down there, there will be no allowances because you start on the Spanish equivalent of an emergency tax code, especially if you start in the second half of the year because you won't be there long enough that year to be a Spanish resident for tax purposes. But that all comes out in the wash when you submit your tax returns.
The real thing to be careful about is the Spanish wealth tax, which could be a pain for someone later in life who has substantial assets. This tax was put in place for a couple of years but I think it was taken away again at the start of this year once they realised they had caused a massive wealth exodus of expats.
Rents are higher than the UK, with an additional 1 months rent equivalent payable in advance to the rental agent, plus 1 month deposit and 1 month rent. Properties are smaller than in the UK, so if you're after something of equal standard then you pay more!
Property size is highly variable, depends on where you want to live and what section of the market you are in. But overall I would have to say this statement is resoundingly not true.
For example, I have a 5 bed house in the UK with a rental value of about £1200 per month. I found a large range of suitable properties within 20 minutes of the airport, in the range of 600 to 800 euros per month. The top end of these typically had the following, shared with a cluster of other houses in a secure perimeter: swimming pool, tennis court, children's play area. Many were next door to the golf course, 10 minutes away from a water park and 15-20 mins from the beaches.
It's a renters market down there.
It really boils down to where you are in life. If you have no children, young children or your children have left the nest it is very suitable. However, if you have senior school aged children then the schooling is an issue for obvious reasons.
The other major factor is if you have a partner, and what they do professionally. Employment prospects are vey poor, especially for non natives.