it was fucking hilarious, every game would have these massive 5-15k gold swings after team fights and the mid game almost completely disappeared, you could literally pick 5 carries and have a better chance at winning than your opponents because a kill on someone who has a streak or a large amount of farm basically gave you 2 whole items. it was toned down a lot over 6.82b and 6.82c but the "comeback mechanic" still exists.
turn rate is a "necessary evil" in dota, it's mostly there to make sure that ranged heroes aren't totally imbalanced and i can see why it's annoying for newer players. a lot of my friends that switched from league to dota found it easier to get adjusted to it by playing heroes with low turn rates like bristleback, slark, sf etc ( http://dota2.gamepedia.com/Turn_rate ). i made an epic long post about it here somewhere before that explains turn rate and reasons why it's good/bad, i'll try and find it.
comebacks happen very frequently which is why i love to watch competitive, so i'll give you a couple of examples. the most famous of which is probably "the play" from TI2. the reason this one is extra significant is because na`vi were the winners of TI1 and at this point of the tournament in TI2, were the last remaining western team amongst a mass of asian teams and eventually they made it to the finals. here's a small clip -
another that springs to mind is game 3 of navi vs tongfu (winner bracket finals from ti3). i won't spoil it, but if you like comebacks you'll love this game.
more recently EG and alliance had an incredible best of 3 at ESL new york, and if you get the time to watch them, i would highly recommend it, especially game 2. if you have the time to watch them then i certainly would, easily the best set of 2014 so far.
edit: also ti3 grand finals, game 5
eg vs alliance, starladder
dota has tons of great comeback games, so it's impossible to list all of them, but these are just a couple of examples, if i think of any more famous/essential ones i'll edit the post.
link to the thread where there was a similar discussion