I cannot comment on SWM, either, because I stay the hell away from it. Not because it's bad, but because I cannot really afford to collect both, not with getting RPG books, too. And I know If I buy only one starter set or booster, I'll eventually feel compelled to complete all the sets. I know how I am.
The game itself is fun enough, as it's something D&D'ish to do when you're only a couple of guys and no DM (no DM required). The rules are mainly D&D combat rules, with many simplifications (level = saving throw bonus) and some changes from the normal game. The first one or two sets didn't look too good, but figure quality has steadily improved with every set (the latest set already released is Death Knell, which is set 6, and the figures are very neat).
Figures are a mix of traditional monsters, newer monsters (and some monsters that were introduced in the Miniatures Handbook, so you might say they're made especially for DDM), and "NPC's" (humanoids or the like with class levels). The races and classes of these NPC's are a mix from classical stuff from the core rules and from current rule books, just like the monsters.
All monsters have two-sided stat cards - one with skirmish stats, and one has an abbreviated stat-block for D&D RPG.
The game itself is fun, as is the fact that you get genuine D&D monstrousities: You get real D&D beholders, mind flayers, ogres, trolls, griffons, outsiders and dragons, not something that "can be used in a pinch". This black dragon isn't just a winged lizard with black paint, it has the typical shape and coloration of a D&D Black Dragon; same with the troll, which is green and has a long nose, it doesn't look like a LotR troll, or anything else.
Personally, I collect them (to the point that I want at least one from every set, but I'm not particularly out to get several of everything), use them for RPG, and make the occasional skirmish game (nothing professional, though.)