I don't see anything wrong with it. There was a LEGO style map for CSS, why not have CSS in Blockland? It's not the same game, it still feels like Blockland and has all the constraints, goofy physics (jumping while prone!), and the look of the game. It's a game re-imagined in a brick world, and it's inevitably shaped and molded into something completely different from TF2.
Personally I wouldn't run a Halo or TF2 server because I have these games and the games are a lot better than trying to replicate the game in Blockland. There is no reason why we shouldn't have a capture the flag or team deathmatch mode though. While I wouldn't run a TF2 mod that tried to turn the game into TF2 as much as possible, I do use the weapons in my own server. Sure, we could leave the weapons in the games. But what if I wanted to have the rocket launcher from Halo and the demoman's grenade launcher in a DM? I couldn't do that in Halo or TF2. The concepts might not be original but the reworked artwork is and some of the weapons have really unique attributes that make for a unique game when you combine them. Especially if you start mixing weapons from different games.
I don't have a problem with content based on content from other games. I don't even have a problem with a CTF with TF2 weapons. The only problems I have are when people are running a TF2 server, where the goal is to capture the intelligence and bring it back. At that point TF2 does a better job of being that game than Blockland and I just go and play it instead. I don't play on TF2 servers. But I certainly do not have a problem with people running the servers or producing the content. I just don't go to them.
