Thanks CC, I'll do my best to keep things updated, without letting any spoilers out of the bag...
Following the two initial 'epic' the dam burst and it seemed as though there was a massive event each year, from DC it was hit or miss, from the solid Invasion, to the poor Millennium, to shooting themselves in the foot with Armageddon 2001 (A brilliant idea. A villain from the future turns ups - Monarch - and it is revealed that he is one of the current heroes. But which one? DC played fast and loose with the story, really building things nicely until it became apparent that the majority of the readership had worked out who Monarch was. In a desperate bid to prove us all wrong, they broke the rules they had set up about who he was, and changed it to a second tier hero. Logic said it was impossible to be him, but it had to stand. For the following months there was the feeling that things were haphazard and rushed, as all the storylines had to change to accommodate what had been done!)
Zero Hour was an attempt to give the DC universe a cohesive timeline, but it seemed, to me at least, that DC just seemed to want to reboot itself every few years. There was a run of Crisis series, culminating in Final Crisis, which should have seen things wrapped up and a stable continuity but...
The return of silver age Flash, Barry Allen led to Flashpoint an epic reformation of the DC universe, culminating in the launch of the New 52, DC's new stable line-up. Everything tightened, interlocked and cohesive. Some of the changes seem to have not gone down so well, and it seems as though there is more tweaking to come.