I am rather new to Minetest, and this is the game that I enjoy most for now. I found many interesting things at the early game:
Smoke: Torches, lava and furnaces emit smoke that generally moves up if it can, and you cannot breathe inside the smoke. This forces you to think about ventilation when building, and conditions your designs (in a good way). I wish there were more features like this that force you to build for some purpose.
Thirst, hunger and "diet": Mobs can kill you, yes, but also hunger and thirst. You need to have reliable sources for food and water. You need one canteen (or more) to carry water. Also, you cannot eat the same type of food regularly because it stops filling you up. That adds variety, it forces you to cultivate different things and/or tame different animals.
Temporary torches: Torches are temporary. Once you put a torch on a wall or floor or wherever, it only lasts for some minutes (they burn out). At the same time, when you carry a torch it emits light. Even if this might seem difficult, it is fun. Light becomes another resource (same as food or water). You need to find other more stable sources of light (oil lamps or candles) but they are dimmer and at the beginning it is not trivial to build them. This forces you to explore and obtain some resources just to have a stable source of light at your first base.
Some say that these increase the difficulty curve, but I'd say that these add some interest and variety. Standard Minetest games just start as "dig as down as possible as fast as you can". For the late game, there is space (where you cannot breath), cloudlands, nether...
Of course it suffers from the "mod soup": Some things are inconsistent and unbalanced. However, the community is really friendly and the developers (which is only one developer) is attentive and tries to iron things out.
And again, for a Minetest beginner that does not have a favourite combination of mods, this game is very good.