It would be hard to argue that NimbleBit hasn’t exceeded expectations for Pocket Planes, its followup to Tiny Tower, the free-to-play hit that became Apple’s iPhone game of the year for 2011, and boasted more than 1 million daily active users at the height of its popularity.

Despite being more complex and strategic than its beloved predecessor, Pocket Planes is already off to a roaring start, amassing more than 500,000 downloads since it was launched on June 14.

We were able to chat with NimbleBit co-founder Ian Marsh over email last week to ask him how the three man team was able to overcome sky-high expectations, a complete revamp, and the infamous Dream Heights to to produce what reviewers are calling their best game yet.

Inside Mobile Apps: Congratulations on the successful launch. Anticipation was very high. Were you expecting this level of excitement right away?

Ian Marsh, co-founder, NimbleBit: You always hope for an exciting launch, but we try not to assume anything and worked hard to get the word out in advance of the launch. Even more surprising is that we’re able to have these kinds of launches with no marketing budget whatsoever! Luckily we’re in a very cooperative industry where other developers help us through cross-promotion.

IMA: Did the high expectations make you nervous at all?

Marsh: Big or small, I think launching a game is always a little nerve racking. There are almost always some bugs that slip through the testing process and you just have to hope they don’t affect too many people and get an update out fixing them quickly. Luckily, I think the launch of Pocket Planes has been pretty smooth so far.

IMA: How many downloads have your games generated overall at this point? How many user sessions are you supporting a day?

Marsh: We’re sitting at 54 million downloads and 150 million daily sessions across all our apps but expect that to jump significantly with the release of Pocket Panes.

IMA: Pocket Planes is much more complex and strategic than Tiny Tower. Did you set out to make a much more complex game? Were you concerned the complexity would put off users that only knew you from Tiny Tower?

Marsh: We did set out to make a game of a different scope after Tiny Tower. Although hugely popular we (and plenty of fans) thought it would be interesting to see the bitizens in a game with a bigger world containing a bit more strategy and choices. We certainly questioned whether it would appeal to a more specific (and smaller) audience, but that never caused us any hesitation. We did strive to make it as accessible as possible to those fans who enjoyed the simplicity of Tiny Tower.

IMA: Pocket Planes took you almost a year to create, compared to four months for Tiny Tower. Why was the development cycle for Pocket Planes so much longer than usual for NimbleBit?

Marsh: We certainly didn’t want it to take that long, but being a tiny team of three we had to shift our resources to supporting Tiny Tower for a while after it won Game of the Year from Apple around the holidays. I also had the privilege of taking a few months off to enjoy the addition of a baby boy to our family!

IMA: Pocket Planes was almost Pocket Trains. How far along were you when you switched to planes? Is Pocket Trains dead, or will it live again at some point?

Marsh: Pocket Planes did begin life as a train sim, but after we had a playable version it seemed a bit restrictive since you couldn’t link any two cities directly like you can with a plane. We also felt that a wider audience could identify with  air travel since nearly all of us have experienced it.  I would never rule out a train based sequel to Pocket Planes, but something tells me we will be bringing the Bitizens to some other genres first.

A screenshot of the now scrapped Pocket Trains.

IMA: It seems NimbleBit was very keen to get user feedback and suggestions into Pocket Planes. You even started polling people on Twitter. How did you test and iterate on the game? 

Marsh: We ran a beta of about 25 people using a wonderful service called TestFlight. With Pocket Planes being one of the most complex games we’ve developed we thought getting lots of feedback often was crucial in striking the right balance. Asking for feedback and suggestions on twitter also served to build interest in the game in the weeks running up to release.

IMA: Pocket Planes is almost much more social than TIny Tower — people literally team up with their friends to participate in the game’s events and form Flight Crews. Why the return to a more social kind of game?

Marsh: I think Pocket Planes might be the most social game we’ve made so far, so I don’t think we’re necessarily returning to one. We were somewhat inspired by the clash mob feature added to Infinity Blade but wanted large groups to be able to compete against each other without necessarily being friends in Game Center.

IMA: With all this popularity has NimbleBit grown at all? 

Marsh: We haven’t hired since we grew to three people nearly a year ago. I think we’re focused on remaining a small team since it has resulted in the development of some very original and successful titles. The real challenge to us now is managing the success we’ve had while still being able to devote enough time to new development.

IMA: Did Zynga’s Dream Heights affect Tiny Tower’s market? Did you see a decline in revenues after the game came out?

Marsh: We didn’t see any drop in revenue and actually saw a big increase in brand awareness for NimbleBit. Perhaps we owe them another thank you note!