Well, since the topic of "how long would the other parts" take came in another topic, I thought I'd answer that question here.
I'll add to what Neil said about us not being able to work full-time on this. Basically, one of our problems with Shadows comes in the form of us being amateur. A lot of times we learned the bad way to do stuff and therefore lost a lot of time. I can say that 2002-2004 were basically our years of learning (even when we are still learning), but it was in 2004 where we went into FULL production. We grew to a huge team, we've learned how to do things, we now know shortcuts we didn't know back then, etc, etc, etc.
So, no, I don't know how long would take "Two that are one" to be finished. I know it is bigger than Shadows. Much bigger. but, like Neil said, we'll only have to add stuff to the engine, we'll know how to do things, we'll have a BUNCH of animations we can reuse, characters, etc, etc.
Also, 2D design is pretty advanced for part 2, so we don't have to worry about it. We'll be able to jump into full production.
Part 3 will be pretty much a breeze. Why? Well... it's complex because of the final stage, BUT, there's not as many characters as there are in 1 and 2, and there's a lot of revisited bgs from part 2. it's shorter as well, goes pretty much into the "action".
So... I hope that answer your questions
