My thoughts:
Cannon seems very swingy. If it hits copper, you've just strengthened their deck. If it hits province, you've just demolished their deck. Admittedly they get that money back next turn, but after that you've put eight trash cards in in the late game. I suppose its nicely self limiting though, as it'll then start clearing out that trash for the player afterwards, but if I were playing cannon, I'd get one, hit a big card, then stop using it.
All in all though, I can't say its over-weak or over-strong. Instinct says to me it should cost 2P rather than 1P.
Battlefield seems to be always better than Estate, but thats not saying a great deal given that a player will rarely want to buy estates anyway. All in all, I think its a very interesting card, as you can't just spam it in the way you would most alt-VP cards. In fact, its probably most comparable to Fairgrounds. I do wonder if its undercosted at $2 though. I would have said $4, as we're always expecting it to be worth at least 2VP, and even with no other green cards other than estate, duchy, province it'll be 4VP. I'd have costed it at $4, to put it in line with Silk Road, which seems comparable in power.
Mercenary is pretty interesting. Again, I worry about the low cost, but its a nice balancing mechanic. Kind of a mix between Militia and Minion. I think in attack terms, its attack is a lot better than militia of course, as the victim can't choose what to hold onto. I wonder if it might work better if it were just a militia-style attack (discard down to 3 cards) but with the changing control effect. The timing is interesting too, as the order of resolution makes it very hard to retain mercs. All in all, very interesting card, and very hard to say whether it is strong or weak without playtesting.
Raiders is a real oddity, but I wonder if its second cantrip effect offers too much board control for its price. I would limit it to trashing non-victory cards from the supply, or up it to $4.
Treaty is Embargo with a shorter lifespan but a little bonus... yeah, works for me.
Archer seems too good for $3, as a double archer opening would make for efficient trashing of your own deck while offering a Super-Bureaucrat attack. I'd say $4, as its benefit is better than Bureacrat, and its attack stronger, but its not good enough to justify $5. I think while its a better card than Bureacrat its fine for it to occupy the same price level though, as its different enough for each to be good in different kingdoms.
Conscription is mini-possession, and is almost too random to be useful. I like it! Good card for $3.
Encampment, I agree with the poster above, should be choose 2. For choose one, I'd not even buy it at $2. After all, you're sacrificing a buy and $3 now for its effect later. Definitely not worth it. Even at choose 2, I'd say its worth only $2, to make it comparable to Hamlet.
Knight is weird. Other players are going to want to discard and cycle victory or curse cards, so you'll normally call action or treasure as your chosen type. Then it all gets a bit head-gamey, especially in multiplayer. In a duel, it becomes quite weak, I think, as the opponent can control what effect you gain, and force you to have spent a terminal action on a small effect. Hell, even if they give you the +1 action, you've still not got a power effect. All in all, $3 seems appropriate, but I'd say that in a duel game, it is a very weak card, and in a multiplayer game its a weak but fun card.
Prize Fight is a terminal tournament that costs $3, and can always be lost. Its... weird. I think i dislike ti for the same reasons I dislike tournament, but its no less balanced a card than tournament.
Tribunal offers a small opportunity for collusion. So does Masquerade, of course, but Tribunal more so. Still, ignoring the funky game effect, +3 cards for a $3 terminal action is too good to me. Compare it to Smithy: thats $1 more for the same number of cards. Does being forced to make this attack make it weaker than Smithy? Personally, I think not. I'd make it $4.
Wall is kinda cool. Not as defensively solid as a moat, but actually a nice way to gradually thin your deck while defending yourself, with the added bonus that you can keep the estates there and use up the coppers first, thus retaining the VP of that trashed card. Hell, because its optional, you can even stash your provinces there. $3 seems kind of solid for it.
My only comment would be that you ought to need to have Wall in your hand to use it defensively (and thus should be used as a reaction in that circumstance). Persistent defence that doesn't need it to be in your hand simply seems too strong for $3, and would mean that if Wall was present, nobody would buy attacks.
Banner is really weird. I like it, but have no idea about its balance. Gaining actions only is an odd limitation though, and I wonder if it could just be gaining a non-victory card, to allow it to be useful in decks that need money rather than just pure engines.
Dungeon is again very hard to judge, but I like it as it stands. My only worry about it is a "dungeon lock" being possible, where the speed at which they return cards isn't enough to give them a hand of cards. It makes Masquerade locks even nastier too. Would this card work if you got back everything in the dungeon rather than just 1 card?
Messenger gives an excellent degree of draw control, but without +card I'm not sure that draw control is worth it for $4. I'd make it $3, as its very comparable to Scheme, in that it might give you more choices than Scheme, but its dependent on shuffle position a lot.
Profiteer kind of relies on good cards being in the trash, but I suppose it sets itself up for that. I guess its self limiting in a way, as your deck gets smaller and smaller, and to get to province you need to go through gold. I guess its also interesting in that if you pur great stuff in the trash, your opponents might claim it before you do. All in all, a really interesting mechanic.
Sapper is brutal in the early game. Open Sapper/Silver. Name a cost of 0 on turn 3, and buy another silver. Gain a 1 or 2 turn lead. For this reason, I'd make it cost $5.
Siege I thought looked like wharf, but on reading I realised what it actually does is much more brutal. The attack portion of this is truly nasty!
I haven't got a great feel for how good this is, but I half suspect it should be a $5 attack.
Soldiers, I think, is brutal enough without the second effect. I'd get rid of the discard and draw clause, as otherwise the attack isn't self limiting enough. I guess it might misfire early game by clearing away their estates, and they can modify their tactics by greening later, but I'm still concerned about the effect of this. Its destructive effect as good as saboteur (fewer targets, but more specific targetting), but for $1 less, and with +2 cards. Either lose the +2 cards or the draw and discard, I reckon.
Cavalry has a really cool base effect, I'm not sure of the $value of the second half of the equation. However, I reckon its overcosted at $5 regardless. Its essentially a cantrip with an effect that won't always hit, and which can be planned against. I'd say call it $4 instead, and maybe even give it +$1.
General is interesting. I wonder though if it could be simpler, and more in tune with the attack theme of the set. I'm thinking ($4, Action) +1 Card, +1 Action. "While General is in play, if you play an attack, gain +1VP".
Gibbett is really interesting, in that it offers the opposition a choice of playing a really weak turn, or losing a strong card, but costs you a card and an action and a card slot to do so. Throwing estates on the Gibbett seems too easy though. However I don't think this is an overpowered attack at $5. This COULD make for low fun though, in that it can make for a very one sided game. A bit like the Torturer effect, but at least thats limited by curses. Maybe as a penalty option add "or gains a curse"?
Revolutionary is like Forge, but cheaper, forced in what you trash, and much much weaker for having to gain exactly three cards. Overall. I'd consider it almost always too weak to be worth acquiring - a strong contender for knocking Develop off its top spot as #1 Worst Trasher. To me, the fix here would be to say two cards and to make it cost $4, thus making it very similar to Remake. You'd get two cards out of it, you'd trash rapidly, and the fact that your deck value doesn't increase is balanced by the increased trashing speed and the ability to go province->province.
Stockpile is entirely fair and sensible. A slow burning money accumulator for $5. Cool.
Tariff is a bit odd, in that its a bit like a lesser effect than embargo, but generates a pile of cash at the same time. I'd consider making it cost $3, but otherwise be unchanged.
In comparison to Embargo, I'd disagree strongly that embargoes are in any way significantly limited by curses running out. If embargoes become redundant because curses run out, the cursed player has likely lost anyway. Multiple tariffs won't break the game, I'm sure. Even if provinces get pushed out of reach, a three pile is generally going to be attainable.
Admiral is Monument if there are no mats in play, which is most of the time. If there are mats in play, then it becomes a very conditional gainer of low value VP cards as well. All in all, a contender for worse $6 card around... Its not even worth $5. It'd be worth $4.1, I reckon, and thats only if there are mats about.
I can't see a way to redeem this card when its so similar to Monument. Essentially, I think it needs a totally different bonus mechanic.
Frontier can only be worth 6VP, and its as hard to acquire as Province. Thats too weak to me. Call it a $4 alt-VP card, and it becomes worth thinking about.
I suppose there's edge cases where it might be worth $8+, but emptying more than 3 piles requires strong engines normally, and that usually means you're either stopping that engine from working by buying Frontiers, or you're getting all the Frontiers on one turn anyway, so the 4+ piling becomes overkill in a case where you'd have won anyway.
So yeah, $4 cost, I reckon, even if this means yet another Ironworks-rush option.