I just bought FS2004 and have been using FS2002 since it came out. In
FS2002 the IFR clearances were pretty limited - precision approaches
only, to the longest runway only at a given airport, no pop-up
clearances - but these shortcomings appear to have been addressed in
FS2004 although I havent played with it much yet.

In general though I would say at $50, it's a no braniner - when I was
doing my IFR training I could only manage to fly once a week, but I
found that doing a few approaches during the week on the sim made a
big difference in keeping the IFR synapses firing. Just counting the
extra training time I saved by doing this 'refreshing' on the sim (and
continue to do) I'm sure paid for the package and the joystick several
times over.

In addition, you can do stuff in the sim that is pretty hard to do in
real life:

1) Shoot any approach you feel like - want to practice an approach
with a DME arc, or a localiser back course approach - just find a
plate somewhere and fire up the sim.
2) Customizable weather - being able to set the ceilings just above
minimums with a programmable variation means you dont necessarily know
if you'll break out above the MDA or not - hard to get that kind of
experience in the air. Or playing with all sorts of wind conditions
3) Quickly shooting multiple approaches - just slew your plane back to
the initial approach fix and shoot it again.
4) There is a flight analysis page you can use to review your
flight/approach and replay it which is quite helpful when you want to
see what those procedure turns looked like, or how well you corrected
for wind, etc. - I guess you can do this with a GPS in real life too
if you have one.
5) FS2004 has a full Garmin GPS simulator in it which is great
practice. I think it takes several hours of practice with these things
to feel comfortable relying on one for a real approach and much of
this can be accomplished on the ground with a simulator, saving you
flight/training time in the air.
6) Pause button.
7) Practicing approaches in the sim before you do them in real life is
great preparation.
8) Practicing instrument/engine failures.

The things that the sim doesnt simulate well are (in no particular
order):

1) VOR and ADF needles dont exhibit course roughness or the same
'analog swing' that they do in real life which makes them a bit too
reliable.
2) In FS2002 at least, the markings on the ADF guage (in the 172) were
poorly aligned so that with the top of the needle on North the tail of
the needle was about 5 degress off South - or maybe it was the fixed
cardinal markings around the guage that were off - but in any case,
you had to do a bit of correcting for this when outbound from an NDB
which was pretty annoying. Might be the same in FS2004 too.
3) Compass error isnt nearly as bad as it is in real life - I'm not
even sure if there is any magnetic dip error or not. Certainly in real
life it bounces around much more than in the sim.
4) Turbulence and wind variation were pretty crude in FS2002 - you
could use it too mess you up a bit but trying to hold an approach
course in real turbulence and changing wind is much harder in my
opinion than in the sim because in the sim it seems that if you dont
react to the disturbance it all averages out and it doesnt work out
that easily in real life.
5) Spatial disorientation and fear (obviously), and when you're making
it up yourself it's hard to create the same kind of
workload-saturation that occurs in real life which is the hardest
thing to handle I think (although having an instructor throwing
instructions at you while you fly the sim isnt too far off).
6) Along the same lines - I dont think you're likely to get an ATC
hold instruction or a request declined, or even a clearance other than
the one you filed in the sim so the ATC side of things is pretty
predictable, but at least it lets you practice managing the radios for
handoffs, etc while your try to keep flying.


Just my 2cents.