I think we're too close to it to tell, which is why I suggested a three-year distance to evaluate events.
In the year after an event it always feels like a lot of new things emerged. Siege created The Heroic Age, with big name heroes being heroes again. It brought Thor's story full circle and him back to the main Marvel fold. It did... um, other stuff? But, in retrospect I don't think it really nailed the "Change the Marvel Universe forever!" hype that most events get.
What has Secret Wars changed, so far? It took the Ultimate Universe off the table, but to 616 readers that's already a non-factor. It moved a number of new characters and concepts into the 616, but we don't know yet if they will all last. However, as I've started catching up on ANAD books, it seems to me like a lot of the big changes in the universe are more a result of having an 8 month gap both before and after Secret Wars for untold stories to exist in.
But, like I said, I think we're still too close to it. Also, maybe for you it really did change everything forever! There's certainly an amount of subjectivity that enters this equation.
To use a similar example - in 2008, would we have said the original Civil War had a lasting impact on the Marvel Universe? And, do we have that same answer now?
Completely agreed. House of M released a lot of concepts into the Universe that cannot be crammed back into the bottle - not just for X-Men, but in terms of the subjectivity of Marvel's reality and also the power level that the heroes are willing to allow any single character to possess going forward.
Ah, but what about the second part of my question - does that make you want to re-read it?
And, as I alluded to above, I feel similarly about Civil War.