Advantage and Disadvantage is a great mechanic my group and i found.
Yep. It's a good one. As Mearls says, it causes
so much clutter just to drop out of the game it's quite amazing.
Weapon Powers is something i like the idea and would have liked to see it more playtested. I was fond of the Halberd with property to knock prone.
I think there's a strong argument for introducing a generic 'hand weapon' for those players who just want something simple that does damage, alongside some more complex "signature weapons" for those players who want more detail. But it might be better if those "weapon powers" only become available to PCs who take the appropriate Weapon Focus (or equivalent), and perhaps fall into some broad categories (so all flails trip, all picks have anti-armour uses, etc).
Concentration is a mechanic i like and i'm glad to see being brought back.
Agreed.
Auto Success is something i'm not too fond of, i like a minimum of randomness. Even climbing a ladder can be failed, that's why we often have dumb accidents in the most mundane tasks we do.
We do, but I'm not sure it's beneficial if the heroes of our games do - Aragorn, Conan, and Lancelot very seldom suffer that sort of failure of basic competence.
Having said that, I'm not convinced it's a good idea to omit DCs less than 10 completely. I think perhaps it's better to list them, but advise DMs simply not to call for a roll at such low DCs. The reason for including them is for scaling purposes - climbing a ladder may be DC 0, but climbing a
badly damaged ladder
in a gale probably isn't, and it may well be easier for the DM to derive
that DC if he's given the baseline one to start with.
Or not; that's just a gut feeling - I don't really know.