The textures are very different although those can be swapped out (albiet with very limitted options if you aren't willing to build the pack yourself). Its more the lighting and shading I don't like. They tend to look a lot more washed out and flat compared to Minecraft. Turning on the more intensive and/or experemental features helps a lot, but falls far short of whats easily available for Minecraft and makes the already iffy performance noticably worse.

In terms of performance, I was struggling to even maintain 144fps on MineTest with regular drops down to 90. I was finding I was getting about half the framerate on average compared to Vanilla Minecraft, with almost no difference running around loading chunks, and a significant advantage for Minecraft in more static areas. That said, Minecraft is a game with a massive modding scene with access to engine-level changes, and using a bunch of the more popular optimization mods mean I tend to be getting roughly double the framerate compared to vanilla Minecraft and four times that of Minetest.

Im sure stuff can be improved, but the userbase and development backing just isn't there as it stands.