I have CFS which I thought was very good at the time.  Is CFS3 up to par?

I think it is. It has imense replay value. You can do campaigns for USA, Britain and Getmany flying bombers or figters and the campaigns are flexible and change acording to what you do.
It's very adictive, you always want to see the next 'map'.

It's much more realistic than CFS, and you will be flying a less 'glorious' war, tactical bombing and strafing ground targets. Shooting down planes is also much more harder comparing the two games in 'Hard' realism setings.

Also it allows you to do team work, assigning wingman to targets etc.. wich is alot more fun.

It has a character developing thing, where you build up your character vision, g-tolerance and health.

If you thought CFS was great you will shurely like this one alot, but be bery carefull, unless you have a fairly good hardware, the game will be unplayable.. 

Sheo, about the Spitfire, I would prefer If I had the old spitfire available, the one with about 1300 mg rounds. This version thing has not enough amo for shooting down more than 2-3 aircrafts :
I even prefer dogfighting with the old Typhoon, aldo slower and heavier it has much more fire power. Last night I shot down a fighter with a single round of.. 40 canon shells carrying 2 1000 lbs bombs. All it takes is a litle more patience 

It sould run it. However I would suggest replacing that gForce2 for a gForce4 before you go expecting amazing graphics and FPS.