Still too easy
Massed archers still rule the field, as in Invasion 2. Only difference is that now it's safer to launch a horde of Infantry on their tails. Un-upgraded infantry at that, since you don't want them moving fast, which is a very cheap solution at higher levels.
It' still far, far too easy. Increasing the number of arrows coming from the defenders at each level was a good idea, but it didn't work out very well. Either reduce the range of archers or reduce their damage more.
The new animation is excellent.
Don't use the function keys for anything in Flash. Many browsers reserve them for other purposes.
All things considered, however, it's noticeably better than the previous one. I'd suggest making another and doing a lot more testing for unit imbalances.