My wife loves 
Police Procedurals.
I'm a 
Firefly fan.
Together, 
we binge-watched all eight seasons of 
Castle!
Prior to our binging, I heard a lot of good things about 
Castle, and figured the show would be something we'd both enjoy. So I bought the First Season DVD set several months ago.   Seven additional DVD sets later, we finally finished Season Eight last week.
The Premise:
Richard Castle is a best-selling mystery writer (and 
Bumbling Dad).  
Kate Beckett is an ace NYPD detective of the 12th Precinct (and 
Broken Bird).
Together, 
they fight crime!     
Yeah, I totally borrowed the 
TV Tropes format for my opening line here.
Anyway, Richard Castle weasels his way into job-shadowing Detective Beckett after helping her and her team of homicide detectives solve a series of copy-cat murders, based on one of his books.  Sparks fly for the first three seasons.  Castle's initial excuse for hanging around was that he found inspiration to 
write a new series of books about Detective 
Nikki Heat--based on Detective Beckett.  By Season 4 romance finally blooms, even though it was 
obvious to everyone around them, that they're a perfect pair. 
In between all the 
will they or won't they? the mismatched duo endeavor to catch the 
victim of the week's killer.
The Good:
What delighted me most about 
Castle were the 
actor allusions to "Firefly."  However, the show went beyond appealing to sci-fi fans.  Just about every episode contained 
shout outs to numerous TV shows, movies and comics. 
I like 
Nathan Fillion as an actor, and what I envied most about his character was his relationship with his daughter 
Alexis.  I found myself imagining being the same kind of dad towards my daughter if she lived with me instead of my her mom.  Of course, without the financial fortune, jet-set lifestyle and fangirls throwing themselves at me.  I also liked Castle's 
generosity towards his new-found friends.  If it wasn't in the precinct's budget--or inside it's rules of ethics--Castle would write a check for anything from paying a ransom to hiring a prostitute (in order to interview her for the case of the week, of course).  He even bought an cappuccino maker to replace the precinct's 
bad to the last drop machine.
  
However, my favorite characters on 
Castle turned out to be 
heterosexual life partners Ryan & Esposito.  On-stage their relationship often mirrored Castle & Beckett's, and from the snippets I've seen, the actors seem to have the same dynamic going for them off stage as well. Each of them had at least one 
day in the limelight episode that was truly memorable.
The Bad: 
Castle certainly wasn't flawless.
As is usual with every TV series ever created, 
the main characters do everything.  In this case, a metropolitan police district's homicide unit was comprised of three detectives, plus a tag-along.  Not to mention putting said tag-along in harm's way on a routine basis.
And since this cadre was critical to fighting crime, we knew the writers weren't going to 
kill off the main characters.  Besides, we had all eight seasons worth of Castle DVDs.  So we found each story to be more amusing and interesting, rather than exciting.
The biggest problem, however, was 
arc fatigue.  
Castle was more than just an episodic 
dramedy about romance, and the 
body of the week. 
 There were numerous story arcs, which took more than one episode to complete, and many of these in-turn, would span several seasons.  In 
fact, half of them were linked to each other in some way or another.  
These shows were 
darker and edgier stories, and were our least favorite.  Watching these required viewing one--or usually more--
breather episodes in order to prepare ourselves for the next downward spiral. 
By the last episode of Season 7, several 
Big Bads have been killed-off or incarcerated, and Richard Castle finally won a coveted literary award.  Things were looking up for everyone else, who've finally become a band of 
true companions...and then they get 
the adventure continues phone call, because another murder has been committed.
This, however, turned out to be a 
series fauxnale.  
The man behind a Big Bad, known as "LOKSAT," emerged.  Most of the stand-alone shows were tainted by the LOKSAT Arc.  Episodes completely devoted to thwarting LOKSAT were tedious to watch, and the season finale 
struck a sour note with fans everywhere.  It was obviously intended as a 
cliffhanger.  But at some point in production, when it was clear there wouldn't be a Season 9, a 
seven years later scene was slapped on to give Castle & Beckett a 
babies ever after ending--and something for fans to coo about.
Except fans reacted with more boos than coos.  So much so, that many (all?) 
Castle fans have 
mentally written-off Season 8 in it's entirety.
TV Tropes has an entire list of 
Castle clunkers on it's 
Your Mileage May Vary Page, along with some 
headscratchers. 
The Awesome:
Overall though, I think the show is awesome.  Just how awesome?  Well TV Tropes has a 
list of awesome Castle moments, along with the 
funny and 
heartwarming ones.
I'm now as much a fan of 
Castle now as I am of any sci-fi or fantasy program. 
Castle now has a fictionalized and even 
defictionalized expanded universe.  That is, there are now several real 
Nikki Heat novels...
|  | 
| (Image:  Cover to Book 1 of 8, with #9 due in 2017) | 
...
Derrick Storm books...
|  | 
| (Image:  Cover to Book 1 of 5) | 
...and 
Derrick Storm graphic novels ghost-written for 
the fictional writer Richard Castle.  
|  | 
| (Image:  Cover to Book 1 of 4) | 
My wife bought me the first two Derrick Storm graphic novels, which I haven't read yet.  I'll probably ask for the first books in both the Derrick Storm and Nikki Heat novels next.
So 
Castle will live-on long past its cancellation.
Castle Sites:
TV Tropes also has a page listing every 
Castle-related trope from A to Z, a 
character page, along with a 
episode recap page (which is incomplete at this time).
In addition to 
TV Tropes and 
Wikipedia, there's the following Castle sites:
Castle TV
Castle Wiki