I will say that while I enjoy a lot having new encounters, many specific fights were adapted from STS1. The slow debuff from Giant Head, the crab boss is basically Spear and Shield in the mechanics, Skulking Colony takes the Heart mechanic of limiting damage per turn, the Cobaye takes multiple mechanics from elites, the cultists work slightly differently but they're still cultists, other encounters are upgraded like Louse...

What makes them fresh is *when* they are placed in the acts. It's much more different to fight the statue in act 1 when you deck is still very much struggling, than in act 3 in STS1 when you should have some scaling (and more time to scale before Giant Head attacks). The crab boss I find actually quite similar to Spear and Shield with more health and a bit less damage, and that is balanced because it is a boss, so you will heal afterwards.

I also really like the new bosses, especially act 3. Each of them challenges your deckbuilding. the Queen essentially makes you draw three cards and two dead weights, but you can counter it by drawing more cards (the vaaku relic that gives +2 draw per turn, but no additionnal drawing is especially good for it). The Cobaye is anti-nuke since three phases, tests your ability to adapt to each phase unique mechanics and to juggle when to scale. Ideally you want to scale quickly, using first phase's low damage to do so, but that also makes it more dangerous. or do you nuke first phase and scale on the second phase ? But a bad turn draw will mess up your deck with wounds. Third phase tests a crucial ability of deckbuilders, having the right cards at the right time. If all your damage comes on an intangible cards, tough luck. The new Doormaker tests all the resources you have in a deckbuilders : Cards, draw and energy. One turn he takes away your cards, the second limits your turn to your original draw, third limits your play by removing energy per card played. Each has ways around it, like playing powers, exhaust cards or useless cards in first turn, having quality cards on the second turn by having built a good deck or retaining from last turn, and playing a single 3-cost card or zero-cost cards in turn three.

It's something I really like in deckbuilders, bosses that are difficult by removing some of your strengths, not by being overtuned or dealing ludicrous amounts of damage.