One of my best solo games is GURPS. This is one set of rules to learn, but it handles any setting, any era, and any point in history I would ever want to role-play in. If I see a movie or TV show and want to play that in a game, it is so easy to create a few characters and dive in. The source-book support for these settings is equally amazing, with books for almost any historical subject, genre, and game you could ever want more detail on.
I played a GURPS Miami Vice style game set in the 1980s and Miami with just the basic set and the GURPS: Cops book for a few police procedures and bits of information.
There is so much great detail on police procedures and cases in the COPS book! For this genre of role-playing, and in any system, this book is an amazing resource.
There is also a SWAT book if you are more into busting drug labs, shootouts, and the more combat-oriented genre play in this setting. If you wanted to play just a tactical team, this is another great book to pick up. I would watch an episode of the TV show for inspiration, come up with a scenario to play, and GURPS took care of the rest.
Maybe we have a bank robbery gone bad, hostages taken, and the characters play a negotiator and the tactical team surrounding the building, and the scenario is to diffuse the situation while the mayor just wants to give the robbers what they want to avoid an incident. Maybe this is a raid on a drug lab in the swamp, and the team needs to neutralize the guards to let the let the narc team in to make the bust. If you were less into the detective side, and more into the action side, there are still plenty of things to do inspired by the TV show (and the music).
Why I like GURPS over other role-playing games is the advantage and disadvantage system. If I give my characters a "mental weakness" that requires a self-control roll, that is in the rules, and my character can have a drinking or gambling problem they need to constantly struggle against. This is great for solo play, since I can setup a realistic character with a unique set of strengths and weaknesses to struggle against, and the game is helping me make those choices and tells me how the character should react.
If a cop character "fired at a kid playing Laser Tag" then he may have a roll he needs to fight against when shooting his weapon at an uncertain target. This can be created in GURPS and gives the character a few more points during character creation, and also defines the dice roll when that situation comes up.
This is great, interesting, Hollywood-level scriptwriter character stuff, and the sort of detail I need to play a cinematic character effectively while playing solo. Other games do not give me these tools, but GURPS does.
GURPS is one of the best solo games on the market, and worth your time to grab a copy of and learn.