Huh. Well thankfully I don't wanna be a MysAd. I hope the games in forum are still running when i am able to get the books.
A quick summary of some major changes:
1) The Edge mechanic is dramatically expanded in use/importance. Many mechanics revolve around Edge, and some "hero moves" require the expenditure of Edge.
2) Armor is gone from the damage soak mechanic. Armor helps you generate edge now (or deny edge to your attacker). See #1 above...
3) Dice pool modifications are not entirely abolished, but are largely replaced by edge modification. See #1 above...
4) Initiative is streamlined by removing passes. Having things like wired reflexes doesn't give you more "rounds within a turn" anymore... what you get instead are extra minor actions for your one round per turn. See #2 above... without armor adding to your soak pool you'll be wanting to spend those extra minor actions on dodging attacks, so these augmentations are every bit as useful as before, even without multiple passes per turn! And of course, more init dice means you're more likely to go first, as well.
There are of course numerous other tweaks here and there. It's kind of a Shadowrun tradition that the Matrix rules change profoundly each edition, but 6e's and 5e's are pretty similar. The major difference being once you have access (marks in 5e) you have it on the entire network, rather than tracking it on a per-icon basis.