MegaBloks appeals to a different market to Lego. I collect the old Dragons stuff and it's easy to see that the terrain pieces are excellent pieces of work. The ice terrain in particular is downright amazing. Then there's the high play value with crystals that unlock secret compartments, altars that rise up with silky smoothness as well as dozens of other clever animations. The Dragon series minifigs aren't so hot as a lot of mine have loose leg syndrome and the non-rotating wrists and hard plastic hands have their own problems too. I still like them though
Not so keen on the older dragons, but the later Ice & Fire series Ice Dragon that I have can be made to glow with eerie icy colours if you press the secret button.
MegaBloks is still a construction set, but not in the same way as Lego is. Not everyone wants to construct every little darn thing entirely out of bricks before they can have the adventure and that's why MegaBloks is more successful with getting licenses for Halo, Warcraft & etc.