Here's my thoughts on this:
1) rain effects: that seems like it would increase lag a bit. Personally, I have found the footprints to be an interesting part of the game, but not extremely helpful in terms of making the game easier to play. It does a little, but not significantly. I see how it could, though. Please make sure that trodden paths are not erased by rain (like the one from quardera town to spawn.
2) Mob difficulty - YES PLEASE. Find a good balance such that players NEED armor if they are walking around outside on the surface at night. You should be extremely likely to die if you go out at night without armor and a good sword.
It is also necessary to balance the difficulty with a reward. So far, I think that the zombies and the tnt monsters are pretty good, just, increase the armor a little. But the flying eyes are way too easy to kill, and they drop nothing. Make it such that if they bite you, you are dead on the spot. Don't increase their hitpoints, just their bite, a lot. Make them drop something nice, maybe a sword, or a time orb rarely, or a mirror rarely (1/99 or something), or 50 food.
One aspect of gameplay should be the ability to make a "job" out of hunting monsters. As such, even on the surface, there should be a range of difficulties, from extremely benign, with a low reward, and high spawn rate, to next to impossible to kill with diamond armor, and a high payoff, and fairly low spawnrate.
The moon is just way too easy, but if you install my VIRON mob, I think that that problem will be solved immediately. The virons specifically protect the valuable ores, and are very hard to kill because they are fast and well armored. I like the fact that you can go to the moon and get rich quick, but there should be a significant danger to stealing the moon's ores. Make sure to set the spawn height min and max to coincide with the moon, in the settings.
I think that the hunger rate is at a good challenging level. It allows you to get some work done, but you can't forget about it. I like it as it is.
I think that the ore commoness is prety good as it is. Just, protect the ores with a variety of difficult mobs.
- Yes, there should be hard mobs underground (need to add more). They should spawn on stone, with a greater likelyhood. You should consider using the mobs_monster mobpack in addition to the ones you have now. They are bretty good. The oerkii and the DM, especially. Or, make new mobs to replace them. But also, need hard mobs everywhere, with an appropriate reward. Just on the surface, they spawn less frequently as underground. Also, you should make hard mobs appear below -50. There is some nice loot to protect from noobs :). But seriously, it will make the challenge fun. Hardcore survival
- Nether mobs: add more types: Pinkies and imps get boring, and definitely you should make it worth the while to kill them, with the drops.
- Slade world- there is some nice loot there, so make some monsters spawn there in order to protect it.
-mars. There should be ancient ruins with good loot that make it worthwhile to explore the surface desert. Also mobs to protect them.
Go ahead and go back over the various mobs, increase their difficulty, either by increasing the bite, the armor, the walk speed, or the spawnrate, or a combo of each. And give each one a nice drop list, with a variety of value.
Also, install the obsidianmese mod that I posted last week. It adds some items and tools that make really nice drops from mobs. The meseapple heals you completely, the engraved sword (no recipe) shoots darts, and the other tools are either pretty good, or they are special in some way. You could even comment out the recipes for all of them, and let all of the items be mob drops or loot chest drops. They are special like that.