Well, the regular Calculus textbooks for most engineering courses are usually Stewart's, Thomas' and a few other Brazilian authors, such as Guidorizzi (which is the closest to Spivak's book). There's a Advanced Mathematical Program in my University which selects a small group of 7-10 students in the whole University to enter and deeply study Calculus, Analysis and Linear Algebra. I was in this program last semester and we used Spivak's for Calculus. Well, I quit because the program taught really deep and pure mathematics and I want something more engineering applicable.
I can't really tell you if it's hard to absorb the material because, as I said, I'm still a freshman. All I can say is that there's a significant difference from High School (in my senior year I had a combined score of 9.7/10 and in the first semester in Uni I got a 7.4/10 studying way more than I did back in High School).
Also, High School is a lot different here. The regular course includes Mathematics, Portuguese, English, Spanish, Writing, Literature, History, Geography, Chemistry, Physics, Biology, Sports and Philosophy during the whole three usual years of High School divided into 20-25 hours a week, depending on the school (as you see, our High School does not split disciplines like Biology into Anatomy, Botanic, Histology, Immunology, etc, but you still go through all that during High School). I can't really say this system is good, as it gets pretty easy, despite the unusual amount of content, though I've heard from some study-a-broad students that it is quite solid.
Also, the best High Schools are usually private (there are some absurdly good free public schools such as Military and Application Schools [held by a federal Univesity]). Opposing that reality, best Universities are usually public and are completely free (which includes Federal and State Universities).
