In a way, you can compare the "war" between Blockland and Roblox to the "war" between Lego and Megablocks.
One has a lot more features, and the other is sort of a minor copy.
I think we all know which ones those are. ;(
One has more movie/game references.
[Roblox has all sorts of "Wall•E" Mods, mods from Jurassic Park, etc. Many kids prefer Megablocks over Lego because it has themes such as "Pirates of the Caribbean", "Narnia", "Pokemon". The other game/company does have some of those such as Spongebob and Avatar, or Half-Life and Left 4 Dead.]
The minor one might have some advantages over the other, but they tend to have more disadvantages [Megablocks don't fit together well, Roblox is laggy.]
end.
i'm tired now...