I've been involved in a large acquisition, as part of the taken-over party, and then became part of the larger entity.
My role was mostly in integration and ultimately worked on the migration of a large customer base onto a new platform, owned by the buyer.
Experience: much as others have said. The one bit of advice I'd offer is: avoid hubris at all costs.
The final, total organisation, after only 3.5 years, ended up being worth only what 'we' were worth when they took us over. The buyers forgot that, while you can take those recurring revenues gathered from the acquired customer base, unless you treat them well then they'll leave.
Which many of them did.
Staff were cut into deeply and redundancies were remorseless, with reliance being on their delivery model to deliver efficiencies. Unfortunately, their delivery model was industry renowned for its inefficiency and inflexibility.
Products from our side of the business were largely removed, and the new parent company's equivalent shoved in instead. We had spent a lot of time building products, had grown swiftly as a result. The final product offering didn't really suit our customer base, and many left.
Result is that the entire entity has not long been bought over by an ever larger entity, who I have to admit, does seem to be spending money and looking hard at where its going wrong. We'll see. They're not hubristic, I note, which reassures me.