Really sorry to say this.......as I live here in North Essex after having moved from London/Hertfordshire many years ago.......but.......
The housing is more affordable because the commute to London (any day of the week) is awful, inconsistent, expensive and slooooow. The A12 & A120 are a nightmare and Greater Anglia Trains doubly so! Don't even get me started on the buses.
My DH (who's from round 'ere) has a two hour+ commute every day in the car from where we live and he's only doing a 50 mile round-trip to Brentwood and back! He often says that the most annoying thing is that you can't deviate much from the A12.......it's really the ONLY way to get there - hence all the traffic etc.
Upshot then is: whether you drive or take public transport the money you save on rent/mortgage you will end up paying in fares or petrol etc. It's so frustrating that in actual mileage from central London it's comparable to living out in Bedford or Oxford but the hassle is so much more living out here. Unfortunately, there's not even that much on offer to do if you're stuck here during the day (except shopping) but it is pretty scenery all round (lots of fields etc.).......and the air is cleaner because of it.......and the schools are pretty decent IF you can get a place near you.......
However.......
in recent years here in Essex, unfortunately.......
there have been major cutbacks to the NHS services, police force and local councils making things more difficult to access properly or at all in some cases. The crime has risen because there just aren't enough police anymore to deal with such a large area (and the crims know this only too well!) so low-level things like burglary, car theft & 'domestics' are mainly un-resolved now because they're having to tackle the drugs and weapons gangs (sounds grim but Essex is a notorious bolt-hole & corridor for such things I'm afraid 
).
Where the NHS is concerned you'll find that because of all the extra homes that have been built (in the last 5 years particularly) they didn't bother to boost the rest of the infrastructure at the same time so the GP surgeries (and schools) are busting at the seams. On average you'll be waiting 3 weeks for an appointment now. The GP's do not do home visits (telephone appts. only) and where we used to have walk-in centres open till about 8pm 7 days a week (all been closed down now!) we now have to go to our nearest A&E (which puts added pressure on them obvs).......in either Colchester, Chelmsford, Basildon or Southend.......and that's the case for the WHOLE of Essex!!!
Although I've got used to how things are here, to this day I still sometimes get 'homesick' when I talk to my family about what they're up to or going to or generally doing etc. My mum moved here a couple of years ago but she only lasted about 6 months before she got completely fed up & frustrated with it all and moved back to Watford! However, she does now fully understand my point of view and way of life now and accepts that if, like my DH and his relatives, you've only ever lived up here and don't know any different (sorry if that sounds awful but it's true!) then it's an OK place to live and work etc.
Also be aware that the salaries (non-retail), for some inexplicable reason, are an awful lot lower up here as well - never did understand that one tbh! 
Our DD's are 10 and 8 now and the other day my DH asked them where they were going to go to college/uni etc. (expecting them to say Colchester - where he went) and in unison they both turned round, gave a tut, rolled their little eyes said: 'London of course!!!'
I promise I didn't say a word.......but his face was a picture! Hahahaha 