I just got my you-know-what handed to me on silver platter.The moment I sent out scouts the AI immediately starting waves at me.I definitely dont remember it being like in the demo.Game is still fun as ever though.I guess I'll just have to build turrets right away.
Might be a different AI personality... some are more offensive, others are more defensive. It's definitely a good idea to get some defenses up pretty fast, though, as the AI tends to show up within 5-8 minutes on average. There are some training videos
here if you're interested. They show one good early build path, including how to recover from some early mistakes.
Or if you prefer a less-harried early game while you're still learning, you could specifically choose some of the more defensive AI types. The Turtles are the most defensive of all, and never attack you with waves (but have incredible defenses to compensate). Or, there are some others that are more in between, like Fortress Baron and Entrenched Homeworlder. You can also use AI Modifiers to have half as many waves if you want. Or, depending, you may want a different difficulty level -- 7 can be vicious at times, so you may prefer to get started on 6.
At any rate, you should be able to tune it to your liking one way or another, so that it's pleasantly challenging without making you feel set upon constantly.