Killzone: Shadowfall - I thought it was fucking aces back when the PS4 launched. I loved the multiplayer in it too, very solid. When I finished it I was shocked to head over to the Penny-Arcade forums and here at the time and seeing that so many people either found it simply mediocre or straight up shitty.
Evolve on the PC. It had some obvious balance issues at launch, and the microtransactions were out of control - but at its core, with a good group of friends, it was actually quite fun. And they improved many aspects of the game fairly quickly. Sadly the population on it went straight through the core of the earth, jettisoned out the other side, and flew off into space never to be seen again, so it took upwards of an hour to find a game even just a few months after launch. Ah well, I had a good month with it.