Oh this is a thread I've been waiting for!
cracks knuckles
Disclaimer: I've been my group's forever DM. I have absolutely no problem with that fact. Being a player isn't something that interests me. Two of my players recently asked to DM a while ago and I've finally played in their games. Here's some things a pretty annoyed DM has to offer:
Rules exist for a reason! Now, I'm not trying to be a rules lawyer here. I play with the rule of cool all the time, but there's just a reason that a Fighter doesn't get 6 attacks every turn at level 5 in 5e. That's broken as fuck, and no "Are you the DM?!" doesn't make for a valid explanation.
Challenge Ratings don't mean shit! Oh what's that? That first encounter of yours wasn't supposed to result in a near TPK? Oh, those three opponents who all have a "save or die" feature are technically on an appropriate challenge rating? Well, maybe you should read their abilities and not rely on a subjective number! DMs need to know what they're throwing at their PCs! When I DM, I throw CRs out the window!
Critical Misses, or why 5e was right to remove them! So, PCs have a 5% chance to be awesome via a Critical Roll. You want to make it so that they also have a 5% chance to succumb to your arbitrary "Crit Miss Table" because you find it entertaining? No, a professional duelist will, in fact, not drop his sword one out of twenty times. "But if you can be really lucky, you can also be super unlucky!" No. The enemy can also be super lucky. Crits can be anything, from being momentarily distracted by unkept hair to slipping in a puddle. 5e did away with them because massively fucking up on your turn isn't fun, and because you slipping up and falling on the ground is something that can happen if the enemy crits.
Realism. Why?! This is D&D! Look, I get that this is a tight hallway and that he's shooting over my shoulders, but being shot in the back because you're rolling poorly isn't fun. 5e has rules for shooting over a target! It gives them an AC boost so you don't ruin your friends day because of your stupid decisions and rolls! Oh! I'm sorry, I didn't realize it was to be more realistic! Excuse me as my character leaves the dungeon mid-fight, running for his life, as he rethinks his entire life, finds a 9-5 job, and pays his taxes like a responsible human being. We're playing a game where a 3-foot high humanoid can achieve terminal velocity by running because a guy in a hood with weird tattoos said some mumbo-jumbo and ate an entire newt's eye.
From my personal experience as a DM:
Custom magic items, because the DMG's ones are boring! Seriously, you have no idea how much fun your players can have with custom-made magic items that fit their playstyles! Get that +1 longsword out of my face, and let me show you my "Gloves of the many-handed" or my "Leash of the taskmaster". Now those were some magic items!
Darkvision, it's stupid, and I hate it! I won't repeat myself, I've made a post about it (Hey, is it really in this sub's current top 25 rated?! =D) already. Feel free to check it out.
Point-buy? You mean Min-Max heaven! Point buy is dumb. It allows way too much freedom to min-max (which is currently a big problem at my table right now).
Roll 3d6 for my abilities?! But then I can get shafted by the RNG! Rolling 3d6 for your stats leads to so much problems with game balance. My first campaign used it. We had the 2 with the insanelly strong characters, and the rest. The rest couldn't do much and most of them said they wouldn't take part in another game where you roll for your stats (which I fully understand. They got shafted. Hard.)
Pre-determined points is clearly superior! I've seen so many people on this thread talk about Point-Buy vs 3d6, but everyone seems to be forgetting the better option: pre-determined stat arrays! Now hold on, let me explain. Stat arrays allows for a mix of min-maxing and balance to be present in your game. You have a Rogue who says he's an ex-military infiltration expert? He can distribute his points by prioritizing Dex, but you won't end up with a guy who dumped his Wis score so his Dex and Cha could be 2 points higher. It also helps to counter the 3d6's "This character is as useful as a paralyzed caterpillar in almost every situation!" because it's a balanced array of points.
Low-magic campaigns require DMs with experience in order to be pulled-off properly. I find that low-magic settings require a DM that's run a few campaigns already. There just seems to be so much stuff you need to tweak and balance to keep the game from getting stale or unbalanced. Because of this, I think it's much better if these are run by DMs who know what they're doing.
DMs can be guilty of meta-gaming! Just because you're the DM, it doesn't make you immune to meta-gaming! A Goblin doesn't know that the Wizard can't cast X spell because he's out of spell slots! If a player can be guilty of meta-gaming, the DM can totally be guilty of this himself!
Tucker's Kobolds is an excuse for DMs to meta-game and use traps! The only way Tucker's Kobolds can be as dangerous as they are is by being prepared for everything, but to even be this prepared, they'd have to have seen firsthand what they're prepared against, which is impossible without meta-gaming on the DM's part. The walls reinforced to block Passwalls, grates to counter Cloudkills, and shutters to turn Fireballs on their casters? How did they even survive a spellcaster being able to cast Passwall (or even know how to counter it), Cloudkill, or Fireball if these spells were so deadly that they warranted their own defenses? Because they know every spells by heart, which requires serious meta-gaming, or a damn good excuse from the DM! I feel like they were just an excuse to get DMs to use traps, which many newcomers consider unfair and unfun for their players. Tucker's kobolds is just a clever excuse to hide the fact that they get to experience with traps and get a feel of which are fair/fun.