I'll comment about this and Flashpoint #5 together, since these are transitional to the new universe.
1. I think the concept of Flash changing the past, with the intent of correcting the present, but not quite getting it right could work. What I'd really like to see is a "What If"-like chain of causal events that explains what Barry didn't get right, and how that impacts the new universe. Just running fast doesn't work for me. He inadvertently changed X, and then that changed Y , which lead to Superman being "reinvented" would work to bridge old and new. There is nothing wrong with an alternate universe diverging based on screwing up something in the past, this has been used in comics and movies many times. It just doesn't ring true here just yet.
2. JLA - it really was kind of flat. Not much dialogue for maybe half the book. Vic Stone new origin - so what? Why cover that in a JLA book, even if he is a member?
3. The whole multi-verse thing. What is the point? Is there a difference to readers between 52 worlds and infinite worlds? Why not just stick with infinite worlds - who cares beyond two or three? And one of these books makes the point that three worlds have to merge? WTF!?! Three worlds? Why? Why even throw this out there. What the heck does that mean - that there are only 50 left after the merger?
I'm one of those old-timers who definitely feel disenfranchised. Did they really have to rub it in? "This isn't your father's JLA". OK, so flip me the bird for being a loyal reader for 40 years. The stories are going to have to be a lot better than this to keep me around in this new universe.
40 years? So you didn't quit during the first Crisis but you're quitting now?