I didn't get into Sims 4 until after City Living, so I'll have to leave out those earliest ones, but the EPs I was most excited for were:
Cats & Dogs - This was the first EP release after I started playing, and I do love me some furbabies!
Seasons - Always one of my favorite EPs in the Sim franchise, weather just makes everything more immersive.
Island Living - I love to play off the grid sims, and this pack just fit in so well with that theme. Plus Sulani is beautiful!
Eco Lifestyle - Again, love off the grid stuff, so I was excited about that.
Snowy Escape - I was only really excited about this one because I'd predicted a mountain/snow pack would be located in a Japanese setting, and I was right! That was fun.
Cottage Living - Probably the EP I got most excited for. This pack was exactly what I was hoping for from a farming themed pack, so I got pretty excited!
I guess the only EPs I wasn't really thrilled about were Get Famous, Discover University, and High School Years.
As for GPs, I got excited for Vampires (it even got me into the game), Jungle Adventures, and Realm of Magic.