Roblox has grown from before. Its rendering capabilitys are still nowere near Blockland's, and physics are bad, (and although I would love a lightsorce) its not putting a limit on your creativity.
Roblox - Free or lowest $6.00
Blockland - $20
Roblox - Make weapons/tools
Blockland - Use better, but pre-made wepons/tools
Roblox - Resize/Add meshes
Blockland - Individual Bricks/Pre-made meshes
Roblox - Sometimes slow/laggy
Blockland - Smooth/Clear Gameplay
Roblox - Full Destruction (unless unwanted)
Blockland - Destroyed bricks dissapear/fall under ground
Roblox - Specialized Editor
Blockland - In game editing
Roblox - Simple fire/sparkles/smoke/explosion
Blockland - Lots of emmiters/lights
Overall:
Roblox - ALOT better for biulding/scripting and generaly createing. It offers (if lag is not present) good gameplay with engine bugs that CAN be fixed by the level's creator. Some bad physics problems. COMPLETE customibility of the game like gravity and background. Better character customization. 4 walls a floor, a roof and a door of any size takes 7 bricks. Free.
Better for the biulder, (usualy) better for the player
Blockland - Good smooth gameplay, awesome graphics and nice weapons. Water is seperated from bricks, light is provided anywere in the map by bricks or player. Good customiztion of character. Bad level creation, no weapon creation, no vehicle creation. 4 walls a floor, a roof and a door take at least 40 bricks. $20
Roblox - It feels almost like a different game every time. With new tools, vehicles and weapons it makes the game be able to support many different styles and games.
Blockland - Try biulding in a pre-made game editor online. I like the ability for lightsorces and its smooth gameplay, but it is completely useless compared to the games that could be made by Roblox.