Shows that started off great and then fizzled out.

Call the Midwife. The first two or three seasons were pretty good, but then it became too much of a soap opera.

I think that a lot of American network tv shows fizzle out as they usually don't end until they are way past done. They have soooo many episodes a season as well. I prefer the 6-13 episode per season shows. I also like it when series end on a high note. Yes we will miss them, but can still think of them fondly.

For me some of the worst offenders were CSI, Criminal Minds, Law & Order, ER, Supernatural, and Smallville.

Pretty Little Liars, Hawaii 5-0, Merlin (Colin Morgan), New Girl, Reign, Teen Wolf, The Big Bang Theory, Once Upon a Time, Shameless, Game of Thrones, Sabrina the Teenage Witch, Charmed, Rookie Blue (Canadian cop show, also airs in US), Project Runway....and those are just the one's I can think of.....

Pretty Little Liars - good premise but they got greedy as FU** deviated from the books to much, and the mystery of who -A is basically made no sense anymore. I just watch it, Twilight style, as an UN-intentional comedy! LOL

Hawaii 5-0 - was a fun show, but then the Danno actor wanted less time on screen for some reason, they got rid of too many well liked characters and boom down the drain. It's still an ok show to watch, but it lost that Steve/Danno bromance. They try to make it up to us with over the top 'carguments' that are not the same organic ones they had in the start of the show. They would argue to solve a case. Now they just get in the car and argue since we need a cargument scene. So forced and it is always about random disconnected bs.

Merlin - Merlin and Morgana needed to hook up, that is all. I know the statement this show wanted to make ...women's rights and such. But I doubt their target demo got the point...mostly younger people. The chemistry between these two was off the charts. Made no sense to ignore it. ALSO no one finding out about Merlin was INSANE, and the reveal was dragged out WAYY to long! Lots of filler bs eps as well....at the start it was so funny ah well....

New Girl - This show got lost in its own 'hipsterness' these people can't possibly exist. At first it was cute, but then got out of control. And the whole Jess/Nick relationship was a mess. Eps are hit and miss.

Reign - The lead female can't really act. Big problem, but rest of cast was so good I just went with it. They got rid of Francis WAYY to soon. And Bash as well. Show makes no sense any more. Enemies are BFFs now...what? LOL Lost the original tension of the show...romance, mystery, magic....etc...

Teen Wolf - What killed this show was ALL the cast members leaving. And I mean MAIN cast members. Leading to a barrage of un-finished story lines, and a revolving door or new un-finished ones. Tyler Hoechiln left for Super girl, Colton Haynes left for Arrow, Adine Kane left for Reign, Gage Golightly, Boyd (don't know his name) both left and went no where...also the darling of the show Dylan obrien reduced screen time so he can try to become a movie star. The show went out of control with new cast members no one really cared about any more.....

The Big Bang Theory - this one has become so predictable, I can tell the punch line before it hits it's so formulaic

Once Upon a Time - KILL SNOW AND CHARMING. That is all, they take up WAYY too much screen time. Please, in a town full of FAIRY TALE characters WHY do they focus on these 2 idiots? It's like going to a buffet and only eating corn....just WHY?

Shameless - show is out of control in believe-ability

Game of Thrones - just wait for him to finish the books, the deviations make the show so boring, also no one cares about bran....

Sabrina the teenage witch - When she went off to college, things got sketchy.....they changed networks and it showed

Charmed - after they got rid of one of the original charmed ones, went down hill from there

Rookie Blue - There are so many cast members in this, but they focus on the Missy Peregrym and who ever she is banging at the moment. At first they hinted at the other characters.....but we NEVER got ANY background on them...but we know ALL about Andy/missy.....ugh

Project runway - reality show i know, but the challenges turned to bs, became more about the drama then the fashion, sad

Charmed
All in the family
7th heaven
Married with children

Luke Cage, Started off great, had great music, things started to fall apart when Cottonmouth died and his replacement Diamondback, he was godawful. Cottonmouth just made so much more sense as a villain and was such a great counterpart to Luke. Diamondback has none of these qualities and falls short as an interesting villain. They should have stuck with Cottonmouth.

I thought I'd be able to come up with more, but I can't.

The only other one I can think of that started out well (not great, but very good) is Life, starring Damian Lewis. The first season was very good, and then became just okay, due to the writing.

Oh yeah, also Lie to Me, starring Tim Roth. Interesting premis and I love Roth. Started out with a bang, and gradually decreased in quality. Never bad, but it did fizzle compared to the first season.

In very recent memory I'd say 'Hannibal" on NBC. First season was great and unlike anything on television, second season built on that and third and final season was a disaster. True, it was near the bottom in ratings all along but popularity doesn't necessarily equate quality. I think it was the best show on TV the first 2 seasons.

Person of Interest. It started off with a decent premise and ended up being a show I really enjoyed watching. I can't remember for sure around what episode it started falling apart, but I seem to remember it being about the end of the second season. The writing style changed completely, they started introducing and developing characters out of what seemed to be a desperate attempt to gain a broader audience or something, it started being filled with more and more nonsensical propaganda, and then it all just went downhill.