1) Working Conditions: Ok, let's be honest here, you are not going to get rich teaching English in Madrid, or anywhere else in Spain for that matter. Most teachers have a second source of income-savings, translating, private students etc. A self-employed English teacher in Madrid will be doing very, very  well to earn 25,000 Euros per year after tax and social security. That's net, into your pocket, after all deductions. And the vast majority of teachers are earning quite a bit less than that.On the one hand, you can still live reasonably OK in Madrid with that salary. On the other hand, a degree is a basic requirement of most TEFL teachers in Spain, so after 4 years studying that salary is nothing to write home about.

2) Climate: It gets very, very hot in Summer, occasionally up to 40 degrees Celsius, but more regularly to 35 degrees. That's why many teachers leave Madrid for the summer. Some take long holidays, others go home to relax, but most go elsewhere ( such as England) to teach students learning English during the summer. Those who do stay in Madrid during the summer, learn how to sleep long siestas and how to walk in the shade.

3) Cost of living:  Madrid is getting more and more expensive. And unfortunately, English teachers' salaries have been slow to match rising costs. English teachers can still have a reasonably good lifestyle in Madrid, but it's more difficult to make ends meet than it was a few years ago.

4) Split shifts: Many teachers work a few hours in the morning, have a few hours off, work a few more hours at lunchtime, have a few more hours off and then teach a couple of hours in the evening. It makes for a long day!  Most teachers try to fill the gaps with private students, but its not always easy.

5) I can't think of a 5th bad thing to say about teaching English in Madrid. Probably because I'm so in love with the city and the friendly people. And how many other capital cities do you know of where you can hop in your car and be skiing in less than an hour? Come to Madrid, earn some money teaching English, have fun and enjoy life in Spain's capital city!