I for one think that FS2004 is great. Mind you you will nead a moderate system to get a descent view. If you just meet the min. system requirements than you might want to think about an upgarde where you can.
I use a pent 3 runs just under a gig a 60 gig hard drive
a fx5200 128 meg ddr ram AGP video card and 640 meg ram I get descent frame rates in the low to mid 20's then it slows down a bit when I max out the weather in a detailed airplane at a detailed airport I still get in the high teens not to bad.
The stornger the system the better it gets. But overall I think the realism is great as well as the 3d views.Be prepared to do a full install as FS runs better when it does not have to read the scenery off the cd. A 3d card is just about a must have one with 64 meg will work
but if you can afford it get at least 128 meg.

Check out the official web site of FS2004 and look at some of the screen shots. Look in the home page of this site and you will find all kind of screen shots they are really awesome