Paper Mario fits the description to a T, though. Loved the first two, the third one was okay, didn't like the fourth one much, but the latest one was pretty good.
Mario & Luigi games are just too much of the same, but were a breath of fresh air once upon a time.
Sonic games, maybe? I think I'm still a fan, but much less so than what I used to be during the Gamecube era. Same could be said about Pokémon, but I still care more about Pokéms than Sonic.
Professor Layton & Ace Attorney: The games became too much of the same, and the stories have become worse than they were at their peaks. I still like and play them, though.
Assassin's Creed, too, went through this, and currently I no longer have any interest in it. The first one was pretty good, second was wonderful, Brotherhood was too much of the same as the previous games, and since then I've had a declining interest in the series.
With Metal Gear Solid I went from fan to no interest. Skipped the casual interest part. Peace Walker just wasn't my thing, and MGSV looked more like that than the MGS games I really liked.
Fire Emblem - My interest dropped pretty hard when they made Fates into three games. The newest game did invigorate my interest somewhat, but not enough to get me excited for the series again.
Super Smash Bros., kinda.I do really look forward to a new entry and play it a lot, but when I've been playing SSB4, it has always felt very similar to its predecessors, so I think that series is reaching that point. Same applied to Mario Kart starting from 8, although bot MK8 and SSB4 felt like improvements from MKWii & SSBB.
Star Fox would probably be here as well, but they do always try something new with the IP, and I'm always interested to see how the games turn out.