Lets see...

STW & MTW:VI a few YEARS! gameplay Very Very Good!

RTW a few months... gameplay poor

MTW2 a few months... gameplay poor

ETW a week at most maybe? gameplay alright, but i dislike the era

NTW just got it recently... gameplay is decent, but i dislike the era

STW2 ??? and ???

FTW ??? and ???

So far about 4 years total playing TW over the years

Replays are your best friend when it comes to getting better and understanding why unit x beat unit y at this point in the game. ;)