When Dishonored 2 came out, it apparently had quite a few performance issues. Users were complaining about stuttering and low performance, even with high-end graphics cards. One post on Reddit grew popular when an employee of Bethesda allegedly tweeted that a GTX 1070 should get ~60 FPS on Very Low at 1080p. The card is generally recommended for users looking for maxed out 1080p or 1440p for the next couple of years, so you might be able to see the expectation mismatch.
The second patch, released yesterday, is primarily aimed at performance optimizations. First, NVIDIA users are recommended to upgrade to 375.95, which was pushed to GeForce Experience and their website late last week. Beyond adding an SLI Profile, Bethesda “strongly advise[s]” the driver to fix a performance bug.
On their side, they fixed an issue with AMD GPUs when cloth is simulated and they now allow those cards to use HBAO+. They also allow the user to limit frame rates all the way up to 120 FPS, although the physics engine cannot handle rates above that, so it’s hard-capped there. This sucks for users with 144Hz monitors, but 120 FPS is pretty generous of a cap if one must exist. Bethesda also addressed stuttering and they fixed the engine attempting to allocate more VRAM than the card has. I’m not sure whether this bug led to outright crashes, or just stuttering as the asset is pulled from system RAM or disk, but either way is quite bad.
If you had a problem playing Dishonored 2, then you might want to try again. If you are waiting to purchase, or have already refunded the game, then unfortunately I can’t say whether it’s all better; I haven’t played it, at least not yet.