Something where the male lead is totally and completely smitten.  Likes to dote on female lead, or likes to spoil her.  Something where the male lead can't even handle how cute she is.  Possessive or not is ok, he just needs to be totally ridiculously smitten.  

Weightlifting Fairy Kim Bok Joo

Descendants of the Sun

Shopping King Louie

I Hear Your Voice

Healer

The Eternal Love 1

Strong Woman Do Bong Soon

Love O2O

Hit The Top (Not at first, however he becomes completely smitten after he falls in love with her. His surprises are the cutest)

Ten Miles of Peach Blossoms- Ye Hua loves her in three different lives (you'd understand if you watch the drama) Warning- You'll hate the second female Suck Jin. 

Strong Woman Do Bong Soon- MinMin is just adorable, the first thing he thinks of her is how sexy she is. 

The Eternal Love- He's adorable, and very much in love. He renounces his two concubines because of her.

I can Hear Your Voice- He has loved her since he was a child. She's older and is not interested at first. 

Shopping King Louis 

5-ji kara 9-ji made (From 5 to 9)- Jdrama- they meet at a marriage prospect date and he is a goner, she is not that into him at first.

Beautiful Gong Shim- No second female lead.  He is a cutie pie. 

Boys Over Flowers- if you like childish romance. 

Protect the Boss- He is childish but he is a goner almost instantly. 

Bromance- Funny 'cause he falls deeply in love while thinking she's a guy. 

Doctors- He loves her since she was very young so he didn't do anything, when they meet again and she's an adult all bets are off. Second female never stood a chance. 

Fight for my way- They are friends for a long time, once they realize their feelings there's not looking back for neither of them. 

Goblin-  Kim Shim was a goner the minute she told him "saranghaeyo" in the first ep. Funny story, I watched this drama with my bf and this is the scene that hooked him lol

Hoo Goo's Love- He has been in love for a long time. No second female lead. 

Lost Love in Times- He falls in love with her twice. 

Love in the Moonlight- He falls in love thinking she's a guy, but finds out soon enough. Second female was never an option. 

 Mars- they both have very dark backgrounds but he's very in love with her. 

Queen In Hyun's Man- That nerd traveled hundreds of years in time back and forth in other to be with her. He even attempts suicide 'cause he thought he wouldn't be able to go back to her.

Strong woman do bong soon was what I had in mind kinda, so good job with those who recommended it.  Thank you all for your recommendations.  Some of these I'd looked at but now I find even more interesting...like shopping king lious.  If anyone has anymore let me know.  I love totally smitten lovers.

I would recommend W.
It's not right from the first episode, but it happens pretty early on.
It's wonderful (':

Of all the ones already recommended, I have to particularly second:

  • Healer
  • Weightlifting Fairy Kim Bok Joo
  • I Hear Your Voice
  • Love in the Moonlight
  • Bromance

Those are all in my top ten and have fantastic, super-smitten MLs.

I'll add:

  • Something About 1 Percent / 1% of Something
  • Sound of the Desert
  • Coffee Prince
  • Live Up to Your Name

All of those are top dramas that have next-level smitten MLs :)