very fun and interesting game, also pretty long.
the battles themselves are pretty easy, as the previous reviewer already pointed out. but that's not a bad thing in my opinion.
producing units, building your buildings and managing funds and oil are just a little bit harder but still not very hard.
then there are attacks that can either demolish cities (you will have to rebuild them) or eradicate them completely (they will be gone forever). that's also pretty interesting and new, so far i haven't seen something similar in other strategy flashgames.
also, the difficulty can vary based on how many countries you control. if you choose to control all countries, it will be almost impossible to win the game (destruction of alien grandmother ship) because you won't be able to build the weapons that you need for that.
overall, it is a pretty cool game, i especially like the fact that it's so long and you just can keep going. i have to say though, when i'm playing flashgames i'm not looking for a challenge. i'm just there for simple enjoyment. so i can see why some people might complain about the difficulty. for me it's actually a plus. i prefer it when flashgames aren't too hard and i don't have to think and concentrate too much.
only thing that might be added is a way to defend myself against the city-eradicating attack. or maybe make a setting that turns them off.
so yeah, overall pretty good game, 4.5/5, will definitaly play again.