This might sound a bit heretical from someone who spent the last eleven years of his life working on graphics engine (just go and look at the screenshots for Flight Simulator X - mmmmm yummy), but you need more than just a great engine to ship product. It'd be nice if you had a reasonably nice one though.
In fact, you don't need a great graphics engine at all.
Just take a look at Second Life.
The graphics are, to put it mildly, pants.
Circa 1996 pants, and that's being generous.
But of course, that doesn't matter because they're not selling to the hardcore FPS gamer, and they are making a crap load of money (and raising a load of funding too).
They're building a great experience that appeals to a lot of people.
Good for them, but the graphics still offend my sensibilities - I think they get away with it because their customer base just doesn't know any better.
And don't give me any of that “but our customers' machine capabilities are all over the map - writing engines that work on the full range of machines from no 3D hardware to the latest NVidia monster is hard.”
Yes, it's hard. But everyone else in the industry has been solving that problem for years. Just hire a couple of decent engineers1.
Imagine what it would be like with an engine with the quality of FlightSim or Guild Wars
Now that would be something to write home about.
1 Well, maybe they have - their upcoming features for the next build of the client claims “now with hardware lighting!”. Whoop-de-doo. ↩