I use to collect Heroclix, and the Fantasy version as well
Mage Knight? Eh...its the comic geek in me that got me into these, and a great deal of other people as well. I just really enjoy Clix. And kudos must be given to Mage Knight by all Clix fans, for being the birth-line of the Clix bases themselves.
I think its safe to say that Heroclix has pretty much got a lock on the miniatures gaming market right now. It appeals to not only gamers, but comic book fans as well, since they are pre-established and familiar characters already--as opposed to some random Elven Archer or a unique Dwarven warrior named Wundabore Fulla****e. The Heroclix characters are recognizable to a much broader market, therefore they attract people to buy them who would never have bought a booster of a miniatures game before...people like me. I had no interest in the gaming world, but was really into collecting action figures and comics. Heroclix was a perfect outgrowth of that. The HUGE character selection (seriously, name a character in Marvel or DC and its probably been made) and added bonus of the game itself was hugely appealing. Add in the over-size (Sentinel, Dark Phoenix, Sinestro) or Collossal figures (Galactus, Spectre, the upcoming Fin Fang Foom which this thread is about) and you're talking a collector's dream!
That in itself was a damn good start. But Wizkids took it a step further to keep the line strong by releasing sets on a regular basis, but not flooding the market (they've stuck to a business plan of releasing 3 sets total per year, 1 or 2 each of DC or Marvel). They listen to the fans (message board chatter, conventions, players at tournaments) in terms of rules changes, abuse of certain powers/characters, what characters they'd like to see, etc. They took it another step further by improving the overall sculpts and paint-jobs of the figures significantly. They went another step further by starting the Buy-It-By-the-Brick only through Brick-and-Mortar stores (and the send-away LE figures you can get through this) and Collector's Sets programs to help bring more money into the B&M stores (and away from the onlin purchases) which hurt both the comic shops and Wizkids themselves in terms of product sales loss. And they continually entice new customers into the game with kick-*** Con Exclusives like the over-sized figures at cons, in addition to their own regular attendance.
Seriously, as a business model, Heroclix itself is a true success. Its by far the corner-stone of the Wizkids' income.