Oolite is an open-source game set in the Elite universe. I spent far too much time playing the Amiga version of Elite many years ago, and I think Oolite's great; they've struck just the right balance between the playability of the original Elite and the realism of Frontier and FFE.
One way in which they've chosen to stick with Elite's behaviour is in how the ship handles: there's no momentum. This is fine by me, since my major problem with Frontier was that I kept flying into planets by accident. However, they've implemented Frontier's engine plume animation, and the faster you move forwards, the bigger your engine plume gets -- which makes no sense, unless they're claiming that the ship really does have no momentum.
I don't think this is the case; by the time of Oolite, navigation systems are smart enough that they're just providing the illusion to the pilot that the ship is momentumless. The pilot doesn't control the engines directly; the navigation system does whatever's necessary to make the real ship do what the pilot wants.
It's therefore fairly straightforward to make the plume animation match reality: just have Oolite figure out what direction the navigation system must be accelerating in, and point the engine plume that way. The result should be quite pretty to look at.
This clears up some of the oddities of the game world. The ship has a speed limit because the thrusters can only maintain the illusion up to a certain speed -- for example, pulling up in a smooth curve only works if you limit the forward velocity. (The fuel injectors don't break this rule, since if you're going faster forwards you need more thrust to compensate.) It also explains why in-system fuel is essentially free -- you aren't using any except when you change direction.
On the other hand, it would also be nice to be able to disable the momentumless interface when necessary (i.e. toggle between the Elite and Frontier control modes). This would let you get a better top speed at the cost of maneuverability, or accelerate to a high speed and then rotate to shoot backwards with your forward weaponry. (Perhaps "advanced flight controls" should be a high tech-level -- or perhaps illegal -- upgrade.)