Great thread! Despite a some slight bias, everyone on here seems to have accurate and insightful points. In that tradition, I will add some slightly biased and hopefully insightful points of my own. As a point of reference, I was an engineering undergrad at A&M and am getting my MBA from Columbia right now after working first as an actuary then in internal strategy consulting.
The first response was a great summary, but misses a few major points.
a) Yes, I would say that engineering undergrad classes are, in general, less technically rigorous. The major exceptions I would note are deep financial theory and economic modeling.
b) At a high-level observation, I would say that a top 5 (can we consider Columbia top 5 for the sake of this argument? I am not here to get into that debate) does not have significantly more difficult curriculum than Mays. However, I would not sell short the impact of fellow students and faculty because, really that is THE difference that drives the quality of any school. I have classmates that have done more before they started their MBA than most of us will do with our entire career. Many have already started and sold their own businesses, others sit on boards of directors, over 40% of my class is international, many have already made (and lost?) millions in the finance sector. As for professors, they are outstanding - and if they're not, students will tell administration and they won't last long. Do you think the textbooks are any different between A&M's engineering program and Tech's? No, it's the students and the faculty... not to mention reputation and recruiting. Which brings me to the most important thing about business school.
So, I would take a long hard look at what you want to get out of grad school before making any decision. That means:
- What interests you?
- What experience do you want during school?
- What career do you want after school?
I learned the hard way that while I am capable and interested in deep technical analysis, what I really enjoy is the abstract problem solving then communicating the answer to executives in a way that can be understood and implemented. Believe it or not, there can be a lot of overlap with the skills you get from engineering - but applied much differently.
Also, I love my experience at CBS. I am gone from my apartment from 6 am to midnight (or later) almost every day and I love it. Some days I'm in class/library all day, some days I'm at recruiting events all day, some days I'm "networking" (that's business school talk for "drinking like I'm 18 again"

all day. Usually it's a combination of all 3. Business school is a work-hard/ play-hard experience all the way. Don't be fooled, it is extremely competitive, just fun at the same time.
Why so competitive? To get the "dream job". So, what do you want to do with your life?!? There are many industries and companies that only hire from a handful of schools. If you want to work for them, you better go to the right school. Even companies that hire broadly are very focused - they might hire 2 people from McCombs and NYU Stern; 50 from HBS and 40 from Columbia and Wharton (totally making those numbers up, but it is the truth). So, in addition to the rankings, etc. be sure to look at what companies actually hire from each school. That should be a huge driver as to what school you go to, in addition to location and where you get accepted.
It's been said enough on here, but don't even think about applying to a top school without some legit work experience.
Sorry for the biased rant, but I am in the middle of it right now and can honestly say that it is one of the best experiences of my life because I know what I want to do with it. If I just got my MBA because the classes were easier than engineering undergrad, I would be missing out on a lot.