I sure hope that they make it a little harder to get into a guild than it was in Skyrim. Here's what I mean:

Joining the Thieves Guild

Skyrim:

*Walks into Riften*
"Hey you! Want to be in the Thieves Guild?"
"Umm... okay, I guess..."
*Puts ring in randoms pocket. Becomes member.*

Oblivion:

*Gets half way through game*
"I wonder how I get into the Thieves Guild."
Imperial Guard - "The Thieves Guild is nothing more than common street thugs and petty scrabble. There is no such thing as a 'Thieves Guild'.
*Doesn't get arrested till near end-game. Gets out of prison*, "Here is a 'note'. Its from a Friend"
Meets at docks at mid-night. Asked to steal journal from a house, but aren't told where the house is, and need to steal the book before the other 2 find it.

Joining the Dark Brotherhood

Skyrim:

*Escapes from the dragon attack at Helgan. Walks into Riverwood.*
First Random I meet - "Hey, did you hear about that little boy in Windhelm. He is trying to call the dark brotherhood. You should go there and do it for him."
"Ooookay..."
*Kills Granny, kills people with bag-heads. Becomes member.*

Oblivion:

*Reaches near end-game*
'I wonder how I get into the Dark Brotherhood?'
Most people - "The Dark Brotherhood is a myth. People say they are a team of assassins, but no-one really knows, sorry."
*Accidentally kills an innocent person* "What have I done!?"
*Receives note day later* 'We know...'
*Sleeps to level-up. Contacted by the Speaker. Gets told to kill old man in remote Inn to become member.*

Joining the Mages Guild (Winterhold)

Skyrim:

*Goes to Winterhold*

'Can I be a mages?'
"Can you cast a spell?"
'Yea...?'
"Cast is on me."
*Casts spell*
"You're in."
'Woo!'

Oblivion:

*Goes to the Arcane University*
'Can I join the Mages Guild?'
"You require a recommendation from all of the 8 city guilds."
'Okay, thanks."
*Spends half the game doing missions for recommendations:
Kills mage bandit, finds invisible khajiit, retrieve stolen staff, retrieve super heavy ring, save wood elf from own zombies, retrieve amulet from bandit infested ruin, get Fingers of the Mountain. lol what?
'YEA! Im finally in the Mages Guild. It was well worth it.'

Joining the Fighters Guild (Companions)

This was actually pretty much the same in Skyrim and Oblivion. Walk in, talk with boss, become member.


TL:DR
Don't make it a derp to join the guilds. Give us a challenge and reward. Make thing hidden. Make things worth looking for. Don't just have every guard in Tamrial telling me that the Dark Brotherhood is recruiting or that the Thieves Guild is 100% known to everyone that the Thieves Guild is "Here" and exists.
Make us second guess ourselves as to the whereabouts.

Although, thats just me and my opinion. Im sure that 80% of casual gamers would just like to be spoon fed their missions with zero effort required.

Now I want to play Oblivion again.

You have a good point, the dev. team of skyrim seemed to run out of steam for the guilds. Lets hope that this doesn't happen with eso.