Yeah, definitely get the 6-pack. MM6 is very similar to MM7 and MM8 in terms of engine and interface, and since it's included in the pack it will give you a good sense of whether you will like those games. And the pack also includes World of Xeen (the giant game made when you combine MM4 and MM5 into one) which is many players' favorite and is a good starting point for the more "old-school" titles. MM3 is also similar to Xeen, but I haven't played it yet. MM1 and MM2 are much older and are too archaic for some, but I still found them to be quite enjoyable if you're willing to put in a little effort (hand-draw maps, keep your own notes, etc.).
By getting the pack, you can pick your starting point... either go all the way to the beginning for some seriously old-school games, or start at MM3 or MM4 for some old-school games that are much more accessible, or start at MM6 to see how you like the 3D entries in the series.
My personal favorite is Xeen, but I haven't played all the games yet... I played 4-6 when they were released, and then got the pack here and played the first 2 games. So I haven't gotten to MM3 yet (will get to it eventually), and I also haven't played 7 or 8.
EDIT:
While there are some overarching themes and lore that carry through the series, for the most part the games are self-contained, so don't worry about playing them out of order.
Post edited March 22, 2011 by Waltorious