I have been through something similar, when my small company was acquired by a larger, established one. It wasn't always easy, but if your team sticks together, you can definitely make a success of it.
Beware the politics, petty bureaucracy, process monkeys and wannabe loudmouths who think they understand the industry though! Sure, people who have worked in big business know how the gears of industry turn, but they often don't understand how to develop good software and keep the quality high. Having said that, you'll probably be able to learn a lot through the experience.
I strongly urge you not to "play up" the notion of "staying for the transition" as another poster suggested. If you give an aloof impression from the outset, you are likely to impact the deal and cause the buyer to reorganize how they schedule your payouts so that you'll have to stay longer to get all the benefits. I've seen this happen.
To be frank, unless you really plan on building a full business yourself with all the right component parts, you'd be idiotic to turn this opportunity down. Good luck!