There are so many things wrong with the thieves' guild that it is actually funny to see people praise it.
My number one problem:
1: The radiant quests are tacked on, and only (apparently, at least in the begining) serve to make you small-ish amounts of money.
2: If I do try the main story for the guild, I don't steal a SINGLE thing, besides one proof of purchase in a safe in the first "real" mission.
3: Too much combat for the thieves' guild. My current character is a thief - he has two iron daggers, just in case he runs into a skeever or something, but he doesn't use armour, weapons beyond the two daggers and poisons planted on the enemy. He doesn't fight huminoids or any enemy that could be considered hard, except for occasionly a paralysis potion planted on them, then run off. In the guild that I'm DESIGNED for -keep in mind that the whole point of the guild is that I DON'T kill people - it's not the DB- and all I do is have to kill people. LIke in the last mission:
Spoiler WIth stealing the Eyes of the Falmer. I spend most of the time killing mobs to get to the end of the dungeon. I'm a thief ffs, not an assassain or an adventurer. And if you have to make me do it, don't give me idiotic companions who mean I can't sneak by!
If I'm playing as a thief, I don't want to have to kill everything.