Can't comment on Mass XXX since I haven't used it.. but I did use Champion Nutrition's Super Heavyweight Gainer when I was in college.
http://www.champion-nutrition.com/c...ight_gainer.php
Got the chocolate flavor. Tasted pretty decent.. Thought it was really, really sweet. Compared to Mass XXX, SHW has 900 calories, 50g protein. Fat is 29g though. But it has a ton more vitamins and minerals and is all natural. Price is about $36 from amazon.