It took me some time before I believed they did anything more than standard work. There are a variety of enemies to face, but most are fought in a similar fashion. You have either land based or flying enemies. Some are big, others small. However, they use a vast array of attacks on you.
Some enemies attack individually while others group together.
Fairly standard shooter stuff, but fun standard stuff. None of the enemies in the game come close to the bosses. These guys are the bad boys of the levels. They are huge and deadly to your tiny craft. One nice thing I liked is the variety you find in the bosses and the strategies in fighting them.