Something he seems to like to do a lot. The design of the levels are all very good and it can be challenging just making it through the levels even without any enemies. The settings for the levels change every 4 levels. They go from forrest to water to lava to ice to desert to jungle etc. It changes the pace of the game and gives you more eye candy to look at.
Water levels have waterfalls that bots hide behind and snipe from.
Lava is hot so if you touch it you will get damaged. I enjoyed that aspect of the game a lot. About your enemies. The game has pretty good AI for it's bots and they will retreat or charge or hide behind walls with cleverness. There are actually only a few times where the designers stoop to the levels of having bots teleport behind you in a cheap fashion.