Oh, ok, but why? :/
Well, first, why I don't like it;
I had a hard time even finding where to play the game. After some searching, I found it. I moved around a bit and spawned some weapons, just to see what they were like. The Roblox rocket launcher is famed for shooting a box that moves slowly enough for you to move in front of it and shoot yourself. I attempted to build, only to be horribly confused by what I was supposed to be doing. I knew I had to resize the brick, but couldn't find out how. So, I simply went back to destroying the starter house. I went to check on a topic I had made here, and when I finished, came back to find Roblox had frozen. I thought maybe I'd browse around their forums to see if there was any help abound, but reading some of the topics made me simply shake my head in pity. I also take into account that although Roblox may be "free", you need to buy a builder's club membership to get decent things, which costs about $300 for a lifetime. Blockland costs $20 for a lifetime.
Second, why it's not best to talk about it;
It usually sparks some sort of fight, and it attracts newer members who think the correct thing to do is to say how much "Roblox sucks Blockland ftw lolol" and simply spill their stupidity everywhere.
I'm not saying Roblox sucks, it just has a lot of issues and doesn't appeal to me.
This is Badspot, the creator of Blockland's view on Roblox:
The web backend of roblox is very impressive but the in-game experience is complete stuff. It boggles my mind how bad it is. Moving around is completely broken - it's jerky, there's no interpolation, you penetrate walls when you run into them, you penetrate the floor when you jump, there is no client side prediction of collision. Shooting is a complete joke - I have literally never seen a shooting mechanic that is worse. The camera goes through walls, gets stuck, jerks around. You can die mysteriously when walking down stairs or jumping into the ceiling. Every build is floating so you often are flung off of the world and fall forever. The character animation and gui look like what you would make in 5 minutes to debug something. With 1000 blocks loaded, i get ~50 fps on my super computer - in Blockland I get like 950+. The whole thing is like a student project that has gone out of control.
Roblox only thrives because it aggressively markets to children who have never played a real game before and thus do not realize how broken everything is. Some of those children happen to be the rare combination of mentally ill and rich, so they pay the $300. Anyone who has played quake, tribes, battlefield*, TF2, HL2, or any real game on the pc simply cannot tolerate how bad roblox is.
Roblox is a financially successful community site and I respect it for that, but it is simply not in the same league as Blockland in terms of gameplay.
Oh, and a wise warning: Posting a link to Roblox here will get you banned. This feature was added shortly after Roblox began the Ambassador program, and we've been told it bans people often.