EU2 is always a worthy buy, Im back playing it at the moment.
To say FTG is an improved EU2 is false. Some things went backwards in my humble opinion.... prefer EU2 battle mechanics and the ability to easily slaughter lowly peasant rebel scum... FTG those rebels fight like Gods.
Two things I really like about FTG were the notifiers and the mouse wheel ability to scroll in and out of the map. When those are the best things...well... you work it out.
One notifier though (revolt risk) causes many crashes, if you have a high revolt risk over many provinces and hover the mouse over it (the notifier) the game completely crashes. There are other things which also causes crashes which never did in EU2. EU2 is a far more stable game (I never really had a problem with EU2 crashing), only sometimes when quitting the game.
FTG adds nothing gameplay wise (except some changes to winter attrition), apparently its a modders dream though and they seemed to be the target market for the game.
Overall if I knew what I knew now and had to choose between the two, Id take EU2.
Dont get me wrong, Ive had a few really enjoyable games with FTG (and perhaps will have some more), but many more with EU2.