I just played on normal, and I finally finished the campaign this weekend.
The third level -- Atwater, or something -- was very difficult and took me around 6 hours.
I am absolutely convinced there was some cheat on the part of the CPU there, but haven't watched the replay yet to prove it.
The other levels were mostly cakey, beat within a short period.
The one that seemed like it should have been a challenge, but was a joke, was the 4-way... I think it was 4th level, right after atwater.
That was a bit too easy.
The last level was. in my estimation, probably the right level of difficulty.
On that last level, you needed to pay attention, but it wasn't extremely rough, and an average player (like me) would ultimately triumph.
As to the strategies used...
Well, on later levels, rushing out the jugs seemed to work pretty well.
And taking the nodes that the game told you to take, that was important too.