Before we even get started, some people might say "Oh, this looks like a Minecraft copy." but that is incorrect, as it was around way before Minecraft was even thought up of. It's not like Roblox either (Ah the famous Blockland vs Roblox wars...) because of the more solid platform and no subscription. So what is this then? Good question. I think Badspot, the creator of the game, can sum it up quite nicely:
"Blockland is an online multiplayer game where you build things with bricks.
It's like playing with legos on the internet."
In my mind, Blockland is one of the best construction/building sandbox games ever made. It is one of my personal favorites that I've played since 2007. I probably have over 600 hours ingame. (Not including Steam) You can do just about anything in this game, from FPS Team Deathmatches to racing to <variable>. Blockland is quite fun by itself, but the real reason you get it is for the high modability. Thousands of community creations keep the game interesting, and populated. Vehicles, weapons, gamemodes, scripts, events, this game has it all for customization. While singleplayer lets you experiment and test, multiplayer is where most people will choose to spend their time. There is always a server up for a specific type of play. (And they usually have good admins)
There is one part where Blockland has an issue...
The community is not amazing. (Most of the modders are amazing though) If you go on the official forums you will most likely see tons of hate/spam/garbage/negativity. The moderators do a good job of clearing out the useless and hurtful stuff, but I feel as if its always been like this. If you are like me, you really don't let it get to you; but I can see how it might be unacceptable to others.
Other than this (really) small issue, I completely and fully recommend Blockland to anybody that is even slightly interested in sandbox games or being creative.