The quality improved a lot compared to its two predecessors that's prolly why this one is more enjoyable than the other two.
As for the story it's the same old recipe with contrived moments to ignite Akihiko's jealousy and spurred him into saying more "suki desu" lines to Misaki, whose tsundereness still hasn't been cured yet after several years of lovemaking with Akihiko. AND this time a new rival not within the Usami family tree appears to chase after Misaki, making him an all-around uke love magnet that's not just exclusive to the Usami folks.
The side couples only get 1-2 episodes each, with the Junjo Egoist team (Hiroki+Nowaki) being the most realistic out of all the couples (at least it is compared to the others).
Since it's yaoi, it's steeped in predictable elements: dragged out storyline caused by misunderstandings and overthinking, that useless "how could a man love another man" statement, using Misaki as a means to get closer to the other crush, possessive seme/uke, clueless uke, and fellas diagnosed with recurring tsundere syndrome (i.e. Hiroki, Misaki, & latest addition Mizuki). Nevertheless it still fares pretty well against other romcoms within its sphere, besides, the comedic moments pardon the aforementioned flaws and keep the story afloat.
ALSO IMO Sekaiichi Hatsukoi> junjou
Junjou Romantica 3 is a wonderful continuation of the other two seasons. The quality had increased drastically, lots of new and improved character design, and more laugh out loud humor. I think this was really what the other two seasons, as wonderful and loveable as they were, were lacking. :)
continuation and worth the watch