What Rinzler thinks of characters
Kevin Flynn - He hates Flynn and resents the power that the User has on the Grid. Rinzler sees him as a false deity undeserving of his status. And where Clu blames the ISOs for everything that went wrong ever, Rinzler very quietly blames Flynn (and the ISOs too, but mostly Flynn).
Note: In the very likely event that Rinzler tries to murder Flynn, the best way to get Rinzler to cut that shit out (temporarily), is to have Kevin bleed a little in front of him. Alternatively, Rinzler catching Flynn in very real physical danger, might spur a protective algorithm or something, but that's a bit dicy to count on.
Yori - She's a vague but persistent memory in the back of his processor that has somehow mutated into a passive obsession. Rinzler projects what little he remembers about her into every female program he meets, and tries to find her in every new woman he encounters.
Clu - Clu is the only program to have earned Rinzler's respect and near trust, but that doesn't mean he holds any huge amount of affection for the administrator. Rinzler likes him yes, but he resents him too. Some days Rinzler is so overcome with the desire to hurt Clu, he is practically crippled by it.
Here's a bit of a hint on Rinzler's motivations towards his absolute loyalty to Clu. << That's a meme comment link.
Castor/Zuse - Rinzler knows Clu and Castor are in cahoots to some degree, but Clu has never bothered sharing his intentions - and for good reason, Rinzler is not a program properly equipped to scheme - but Rinzler dislikes Castor anyway, finding him treacherous and untrustworthy. If Clu asked - which he doesn't - Rinzler would advise rectifying the guy. He assumes Castor is too dangerous and too much of a nuisance to keep around. Especially considering his past transgressions.
Tron - Scraping up what little he remembers, Rinzler mostly pities and is embarrassed by his old version. He also resents his past self for being mentally weak, and not fighting to see past his old ideologies.
Anon - Rinzler never had a chance to meet him, but from what little he's heard, Anon sounds like a right pain in the side, and is a good example of all the trouble a member of the resistance can get up to, and how much they can set back the system's progress. Anon doesn't however strike him as sounding like much of a threat - just some punk program who he'd liked to have had the chance to put in their place.
Gem - Rinzler likes the sirens by association because he sees them as belonging to the games. He also understands that the sirens are attractive - in so much as he acknowledges that sort of thing - and he approves of her in a distant sort of way because he assumes she has some hierarchical power over other sirens. He is vaguely suspicious of her, given Gem's company with Castor, but because she is associated with the games, he's less inclined to think she's any sort of risk to the system/Clu. That doesn't mean he wouldn't be any less ruthless in dealing with her as a threat, he's just more prone to ignoring her.
Note: Given Rinzler's position as final boss for Disc Wars and given the art book's comment on what the Siren's represent, Rinzler has his own personal siren than attends to him before and after the games - if he chooses. She's unnamed, and they don't always live for all that long. For varying reasons.
Quorra - Rinzler has no interest in what the ISOs represent. To him all Quorra stands for is a loose end that needs to be remedied, and she irritates him because she's the one that got away - and continues to get away. Quorra's existence is kind of like a reminder that there are still imperfections floating around that he himself hasn't been able to take care of. And he would like very much to do nothing more than 'take care of' Quorra permanently. He doesn't however consider her a threat at all.
Sam Flynn - Sam is just another User, and further proof that humans refuse to follow established rules and social norms. This makes them dangerous, and also unattractive deviants. Rinzler further dislikes Sam because of his connection to Flynn, and sees the boy as an incompetent version of his father - though he doesn't completely understand the relationship between the two.
Jarvis - Rinzler understands that Jarvis must have some redeeming feature or usefulness - because why would Clu put up with him otherwise? But whatever Clu sees in Jarvis, Rinzler doesn't. There's a silent competitive animosity between the two, and Rinzler thinks Jarvis embodies everything that is weak and useless in a program. Secretly though, Rinzler understands that Jarvis is better equipped for logic, tactical calls, and ... thinking. But that's not something Rinzler relishes contemplating.
Alan Bradley - Alan is a User Rinzler has washed his hands of. He doesn't think Alan is worse than Flynn because at least he isn't parading around letting programs worship him, but once upon a time, Rinzler imagines Tron would have liked Alan to step in and save the Grid from Flynn's callousness and cruelty. (Keep in mind, Rinzler harbors insane bias and devours propaganda.)
Ram - Plain and simple, Rinzler doesn't remember Ram. Or rather, any camaraderie or friendship they shared, he's lumped into his feelings for Yori. Or more accurately, what he wants to believe is the entity that he's created to stand in the place of what Yori meant to Tron once - because at this point, what Rinzler has convinced himself he remembers about her, isn't all based on actual fact.
Abraxas - Abraxas came and went before Rinzler's time, and he wasn't a project anyone ever discussed with him. Probably for good reason.
Others - (as I remember them)