Hey all, I've finally played GoA and I've really enjoyed it.

I've stumbled upon this situation and I didn't know how to solve it - the Gate Box artifact instructs you to draw 1 Other World card and place it below the 6 adventure cards. GoA, however, has changed the mechanic with the use of the gates. Should I play the Gate Box RAW (just spawn a new OW card), or treat it merely as opening of a gate, following those rules?

Glad you're liking the expansion

Indeed, you have to add a gate every time an OW card enters play if you're playing in the Streets of Arkham mode!

This highlights an important shift in the role of otherworlds from the base game to Gates of Arkham.

In the base game, generally opening gates to otherworlds was a good thing. Thus, they functioned like "rewards" -- indeed, they often appeared as rewards on tougher adventures. They gave you an additional choice of adventure to tackle and almost always offer elder signs (and sometimes doom reprieve) as rewards. The gate box could often be used right away without any thought. Having lots of gates open is great! More choices, more Elder Signs available!

In Gates of Arkham, otherworld adventures are a mixed bag, but now gates are thought of more as a "penalty". They tend to be bad now because if you have too many open, you run the risk of lots of monsters spewing out, or the mythos / ancient one punishing you for having gates open. They also lock down Arkham adventures while the gate is open, which is another problem. However, the motivation for opening them is the same as before -- you want the Elder Signs that they tend to offer. Now you have to be a bit more careful and control how many gates are open.

I'm inclined to say that the Gate Box and Find Gate items should still have some element of benefit to them, as befitting an item, even when using the new gate mechanic. To that effect, I play it that using those items allows you to place the OW face-up from the start, rather than face-down (while still spawning a gate). Obviously a house rule, but a (relatively) minor, and thematic, tweak, I think.

Edited for clarification....

Yup, has sense: at least you know what you're summoning by using a specific item. Kinda difficult to code properly in the rules; that's possibly the reason why a single rule was chosen for all cases, I think

Yeah, you'd want to print up new cards for those 2 items clarifying the wording, rather than make an exception in a rule book. Perhaps one for a future FAQ, should it become an official ruling....