I am in the same boat. I added Horse Lords, and was looking at Conclave. I had avoided WOL due to the broken seduction mechanic. Have they finally reigned that in with the seduction rejection balancing? Also, Conclave certainly looks like it would make the game more realistic, but does it also make it a lot less fun?
Yes, seduction was basically fixed in the 2.5 patch. You'll frequently see wives and such with the "Rejected Seduction Attempts" modifier as well, which is a sigh of relief for many.
With Conclave, it was intended to be a difficulty hike for vetted players. The education system is sort of a hit or miss with most people- either they like the idea that super-good heirs are a rarity and like being very involved with making the educational foci choices or they hate how random and micro-intensive it is. The council mechanics are also sort of like that as well. Some people think it adds depth to the game since you have to fight back and forth with your Council using favors, wheras others aren't a fan of the idea that your Council is more often than not is going to be your greatest enemy if they have any power. Things can also get a bit ridiculous if they have full authority and you can't even hand out titles without incurring some tyranny or you have a vassal with high opinion in the malcontent faction.
However if you play your cards right, you can actually make things very easy for yourself once you figure out that if your Council is content and your other vassals have NAPs with you they can't raise a hand to you at all. I also personally figured out that if upon succession your Council demands to be empowered, you can just accept their demands then use favors after the timer is up to revert the law back to unempowered indefinitely until you've become a large kingdom or empire.
Regardless, most of the hate Conclave received was more aimed at patch features such as the threat and defensive pacts system (which can be skirted around if you just pace yourself and let the threat burn off after every war). It's a decent DLC that needs a little bit of refinement, but it'll probably be your worst nightmare if you're a map painter or a greatly needed extra challenge if you're fully vetted.