For being such a staple card introduced in the Core Set, I've never loved this card. The primary reason is that it costs 4, i.e. your whole hand. You generally want to play the Mansion as early as possible for maximal effect, but that means you likely don't have resource generators to help with the cost, meaning you are spending one of your critical early turns doing nothing but playing the Mansion. If you can eat the cost of a Villain Attack, the gained Threat, an extra turn with a Minion out, or Side Schemes doing their thing, it's usually worth it.
The problem is that in some scenarios you just can't afford to take that kind of tempo hit.
Once you play it, it's amazing to have out. An extra card is not simply another resource, it's another option to deal with the situation at hand.
A primary caution is that you do NOT want to have it vulnerable to being discarded by Caught Off Guard.
I'm on the fence on rating this card.
It's either an A: Provides extra cards in a game where card draw is king. Provides an additional option every turn instead of simply more resources.
or a B: Avenger's Mansion is now an option among many options for extra resource generation, and with the availability of 2-cost resource generators and the Quincarrier, the Mansion may be too expensive for your particular Hero.