As you have already noticed, opinions differ. :) It's a matter of taste but... even though some people think that Nirvana in Fire is slow and/or boring, my impression is that most people really love it. It's epic, it's true!
For me Nirvana in Fire is the best drama EVER (I've not watched as many as some people but I do have 100+ on my list) because of the excellent acting (so many great actors) and the amazing characters - even the ones you don't root for because they are "on the wrong side" are like real people so it's a joy to watch everything. The plot is also very, very good! Even if there are some things you sort of can figure out from the start I found every episode so captivating because it's all about the journey! If you like a lead who is super intelligent, real bromance, power struggles, really good female characters... you'll love it. It's long but it's so worth it and I even wanted it to be longer.
Battle of Changsha is also very, very good. It's more realistic. It's a war drama but it's also a heartwarming family drama - it's more about that than about action but there are battle scenes and exciting moments! A pair of twins is in the centre of attention but soon enough you'll find that you love and care about all the characters! There is also romance in this drama.
I have watched four or so episodes of Boss and Me. I know lots of people like it but it wasn't for me. I couldn't stand how controlling the guy was and I just couldn't like the girl.
Aside from NiF and BoC, I also love Ode to Joy (female friendship, life, a bit of romance - it's wonderful) and The Disguiser, a spy drama. If you prefer something light and youthful maybe you would like Go! Goal! Fighting! I'm currently watching Sparrow (another war and spies drama) and Surgeons and I like both of them.
Oh, and if you like romance I definitely recommend Sound of the Desert!!