There's a lot of wriggle room in what counts as checking out. For instance, some franchises I'm still interested in, but never got round to playing. But I guess I can nominate:
-Mass Effect: Only played the first. Wanted to play the second, but my 360 succumbed to the red ring of death, and it was years before I got another one. By this stage, I knew the storyline, and RPGs, by their nature, are huge time sinks. Coupled with how Mass Effect is meant to be replayed across an entire trilogy to account for various choices, and, yeah. I'm just wary of committing to such a time investment. It's kind of why Andromeda appeals to me, in that I can play it without having to worry about the previous games.
-Mortal Kombat: MK1-3 were "da shit" back in the day. However, I never followed the series after that. Just kinda lost interest.
-Pokemon: Never went beyond Gen 2. Similarly, just lost interest in the games/setting.
-Resident Evil: RE5 was the last game I played in the series. A good game, a bit too actiony, but I enjoyed it. That said, I didn't go beyond that. I felt that the storyline had been concluded satisfactorily, and seeing RE6, and other spinoffs, I could see that the series was moving away from the originals too much for me. RE7 looks interesting though.
-Sonic the Hedgehog: Last game I can recall finishing was Sonic Rush Adventure. But as I grew less interested in the comics, and how I got Shadow, then Sonic 06, then Unleashed...yeah, I'm not really a Sonic player anymore. To be honest, the Sonic Boom cartoon is the best thing to come out of Sonic for quite awhile for me.
-Star Fox: Coupled with Command being a piece of Tricky fodder, and Zero being on a console that I don't own, with motion control gimmicks, and rebooting the series AGAIN...yeah, I'm not onboard anymore.
-Warcraft: Well, sort of, in that I enjoy the RTS games (well, WC3 & 3 at least), but don't enjoy playing WoW. I do what I can to keep up with the lore, but wikis are only going to convey so much.