When building a "first person shooter" game similar to Doom 3, Quake 4 or Crysis (on a licensed engine), how much time is it going to take, including engine tweaks, 3D modeling, level building, and testing, assuming there is a team of capable software engineers, 3D-modelers, level-designers and testers.
And is there any significant difference in development time between PC and console games?
There are too many factors to provide a good answer.
It depends on the exact requirements, knowledge in the area, experience, number of people, and so on.
Short answer: More time than you think.
Long answer: If you have to ask a question like this, then you are not ready to make a FPS.
Go read everything at GameDev.net and you'll understand the complexities of game programming, even when leveraging an existing engine.
I've personally never done this, but I imagine that developing for a PC would be take longer due to the many flavors of hardware out there. Consoles are pretty locked down, you can code it for one type of machine and be confident it will work across the board.
I'd be prepared to spend a very long time on it too :-)
Roughly, think in terms of person-years of effort. Popular commercial games have fulltime teams of developers, designers, artists, writers, etc.
These days (end of 2008), a big FPS game takes 10-30 million dollars, 1-3 years to develop, and 50-200 person team. Even on a licensed technology.
A very small FPS shooter might be done in a few weeks by one guy, of course.
The major part that makes modern games so complex is massive content amounts. A character in a game might need thousands of animations, for example. A forest might need thousands of different trees to me made. Tens of thousands of sound samples. And so on. However, content authoring scales quite well, so if you can put a 1000 person team cranking out content, you can expect to make it faster (your question asks about time "given the team", so I assume time is the most important metric).
Developing on a console is easier in some ways (much less hardware configurations to worry about), and harder in other ways (fixed set of memory, slower CPUs, exotic tools, higher initial investment because you need a devkit, ...).
But like someone else said, if you ask those questions then you just didn't do your homework. Go look at gamasutra.com, gamedev.net, igda.org, edge-online.com to get some grasp on the industry.
You might want to look at Microsoft's XNA API -- it will run on XBox and PCs, and it's very easy to get started (lots of samples).
http://msdn.microsoft.com/en-us/xna/default.aspx
There is no way to tell you how long it would take, but you should be able to find a sample to help you get started quickly.
I remember back in highschool we used a BASIC variant Dark BASIC to do some games designs.
If you don't mind god-awful graphics, there was a tutorial in this to build a simple FPS.
Start to finish, doing little more than copying the tutorial samples, you could probably have something up within a couple hours. (This is, mind you, just a copy/paste job).
If you want something more modern you're probably better off just modding your fav FPS. last I checked it's pretty common feature nowadays.
I would say that with a full fledged development team working full time, anywhere from 3-5 years, even longer (duke nukem forever, for example ;) ). It really depends on how much content you want in it and how much detail you are going to put into it.
Crysis took a while to come out, but crysis warhead was released only a year after the original. This is probably because the engine and most of the graphics were already done. Still, it took about a year to make a 6 hour single player campaign.
Most modern games take about that long from concept to release.
Building any game is not a trivial thing.
Developing for consoles you are really at the mercy of the manufacturer of that console to provide you with the proper information. Some consoles have failed due to the complexity of their programming (sega saturn i hear was shocking)
On the other hand, XNA for xbox360 is a nice bridge between pc and console.
You can just go check the blender engine (check some docs here), maybe this is what would help you to develop something faster.
But in fact, and trying to anwser your question: try making a spec. I know most hate it, but it's a great thing when thinking of how long it takes. When thinking of the spec you'll ask yourself some questions that would show you how complex it is to make a game. One of it would be what engine to use (or write your own). And choosing engine will partially anwser some more questions, for example: should the movement of player character affect the velocity and trajectory of bullets?
There are tons of things you might not have thought about and they will suddenly pop there as you sit to work on your spec, and later to talk your spec through with someone. So if you got any estimates right now, multiply those by any factor between 5 and 100 and you'll get the anwser.