I figure I'd better say what's on my mind before you get too deep into creating the next version:
Furnace suffers from Rock Syndrome, an acute disease caused by the overuse of rocks as cover when it's just oh so convenient. Case & Point: A. It's very bad... there. You've definitely created what I can say is a nearly flawless battle area in terms of no overpowered angles, but that doesn't make it fun to play...
Gravelpit, to hark on what I consider the quintessential TF2 map, does the same thing with around half the number of rocks and probably a quarter as much cover overall. It's remarkable, yes, but on Furnace you've basically done the same thing. It's like being wordy or loquacious... to solve, at least make some of the rocks... not rocks? It may just be my OCD, but it's always bothered me. But as it is, I think one of the main things holding this map back from Gravelpit level awesomeness is its overuse of cover to make up for what would otherwise be called... poor planning.
A, just in general, should be bigger. Adding conflict-creating areas towards the front of A, by that I mean clearings or something to bring the fight away from the point, will make the experience of A much more crisp.
As far as detailing, just don't go overboard! I LOVE your aesthetics, don't just widen and prettify because you can. It's very understatedly... majestic, right now, with this entire run-down area bathed in the glorious sunlight.
Much <3,
FoXy