In a nut shell..
Hardest thing I've ever done but despite everything I would do it all again to have the family we have now.
Top points to note IMO...
It's 'parenting plus'. You're a parent as much as any other by any other means, but it is not the same as parenting a birth child, get your head accepting that and you're off to a good start.
You are not going to fall in love with this child from day one, then add in the fallout by that child of moving once again and the insecurities that's caused, plus any other trauma they are dealing with linked to the reasons they were removed and everything being new and not familiar. You've now got a child you're not bonded to by hormones, tantruming, often including head banging and lashing out, they're not sleeping, so neither are you, but then they are glued to you the rest of the time so you can't even so much as go to the toilet. The love comes but not overnight. That's hard, really hard.
Contact with birth parents is pretty standard, even if you're writing to them each year and they're not writing back. You'll end up wanting desperately to have it flowing in both directions once you have a child placed with you, for their sake, but when you start the process it's the hardest part to accept (IMO!).
There is something known as the BS case, it's recent. It hasn't changed the law but it's made SW's nervous. There was apparently some sloppy practice going on and this ruling was supposed to re emphasize the need to make sure adoption was the absolute last resort in all cases. The number of children being placed for adoption since then has dramatically dropped, as while it may have gotten rid of the sloppy practice, it also seems to have ALLEGEDLY made social workers more nervous at choosing adoption as the next step. Add this to a speeding up of the adoption approval process and you have more adopters than children waiting. If you are not out to adopt a school aged child, a child with significant extra needs or siblings (unlikely to get approved for siblings if single, though not impossible) then you COULD be in for a long wait, so be prepared for that wait. Our LA has recently advised 3yrs+ for some adopters! But things change, as quickly as the numbers have dropped, something could happen to turn it in the other direction.
The 6 month approval process seems scary and invasive but it's not that scary and it does need to look at every aspect of your life for the child's sake. I think the majority of adopters, under the new quicker approval system at least, find post being approved, while waiting for a match, far harder. It's horrible for you because, rightly so, it's finding homes for children not children for homes. Therefore you will literally be compared to others adopters, what you have to offer vs. what they have to offer and it's hard when you're not chosen, which for some at the minute is happening repeatedly, as there can be 50 adopters to choose from for every child.
If you're single (I've made that assumption based on 'ex-partner', sorry if I've assumed wrongly) you'll need a really good support network of friends and/or family. In fact, if you're not, you'll need it too! I have no idea how single adopters do it (but they do and do it well!). And yes there are millions of single parents out there, but I refer back to point 1...parenting plus!.
Having said the above, you then need to make friends with other adopters, as while your friends will tell you everything your child does is the same as their 3 yr old, so it's normal, they will regularly forget that their 3 yr old has had a great start to life, so of course their child is going through 'normal" testing of boundaries etc., yours however has experienced serious trauma and it is therefore highly likely to be a factor, so yes it is different! You'll get good at the 'nod and smile' 
Be aware, if sorting finances out now, they will want you to take a year off work and ideally only return part time. Well, ideally not at all, but that's not realistic for most of us! Having said that, they want to know you will give up work should the additional needs of a child mean you need to. We all see the child crying for mummy at nursery when she leaves but they get over it in 10 mins. Try a child whose parents have left and never returned, their concerns are real not theoretical and for some adopted children, nursery can be just too traumatic for quite some time.
Social workers...We've had really good ones, others have had horrific experiences. You do have to face up to the fact your life is in their hands and it seems pot luck on who you get 
Post adoption support, I'm yet to use but I'm dreading needing to based on what is written on here!! Someone recently quoted a 1/3 of adoptions have no major problems by teens, 1/3 have some problems and the remaining 1/3 have significant problems (or something like that I think), so chances are you may very well need to. A failing system of support will probably be the scariest thing to hear but you need to go into adoption with a real need to fight your child's corner, because there is a real possibility you will have to.
Now, if you've read all that and aren't put off (I wasn't trying to!!!) then this is very likely the path for you! 
What I can't sum up in words is the positives. Our life is the most challenging it's ever been but the happiness and love that they bring is imeasurable and indescribable, you can't put that into a sentence. I can't imagine being without them, it feels as if we never have been. I love them to the ends of the earth and for all the process took out of us and for all the additional parenting things we have to do, it's 100% worth it for the family time we spend together, that essentially is as normal as any family time experienced by the 100's of others versions of what makes a family unit today. We chose this route to becoming parents over IVF and I have zero regrets.
I strongly recommend the previous advice of reading through the many threads on this forum. You will really get an idea of the various issues you may experience and what 'parenting plus' really means
Good luck!!
(LONGEST. POST. EVER.
Sorry. )