I could not really join any multiplayer server (it told me that "the connection is not secure"), but let me share my thoughts anyway.
It's a pretty solid base for a Minecraft clone, if not in very early development. I dig the graphics, honestly. They look really good and original, compared to a lot of those scuffed Minecraft clones you see on the web. This includes the inventory - it looks kind of neat! There's no sounds, I guess. The movement mechanics, I dunno how to rate. Read below why. The worldgen is not featureless, either - it works fine and the chunks load fast. I stated it is featureless before, but I played the game a bit more and it's pretty good.
I like that the early creative inventory allows you to switch pages of items, although it is slightly annoying how when I want to switch blocks, I HAVE to put the one I'm holding in my cursor into an empty space. At the same time, I've noticed how even if I don't do that and just leave the inventory, it still stays on my cursor when I return to the inventory. That's some good forethought. The game's performance is surprisingly good, also. I'd have expected this to melt down my computer the second I turned it on, but no, I'm playing it on Firefox with no fear! It's in the hands of a VERY competent developer.
Now, here's some actual issues:
My mouse keeps sliding down while I'm playing, for some reason, and pressing Space both makes me jump and slides down the page. I think all of those issues are a result of putting the game on a website. Sometimes the mouse buttons don't do anything in the game unless I load a new chunk, which is probably also a result of that. Also, it would be really neat to auto-save the worlds - every time I refreshed the page, my world was simply not there. Although I am glad you can just save your world, anyway.
That's all. I would LOVE to give it more stars. There's just not much this game has to offer now - it's basically what if Minecraft Classic was uploaded to Newgrounds. On the other hand, it's really functional, even at this early stage, so maybe it's worth keeping it around until it's updated? Honestly, you should probably upload it when it's more finished, though, because I feel kind of bad giving it this score even though you put so much work into it. I'll definitely change the score when you add more features to it, though!