It recently dropped in MSRP and has been getting cheap? Possible monthly candidate? I fakeybro'd it quite a while ago and barely touched it. Story of my life.
There's plenty of endearing criminals in media. Even if they're not endearing, there's other ways to make you want to play them or make them likeable in some ways. Trevor has none of that.
Characters don't always need to be likeable, IMHO. While in many cases, it will help many players to actually make them like-able - eh, depending on the story, plot, characters, and any other points the game makes (especially when it's satire), etc etc - some might be able to get away w/ making someone not like-able.
Michael did something to Trevor, in their past - from a story and character stand-point. Story and character-wise, you need that mission & scene especially, to understand...why Trevor's, more or less, a lost cause here.
Deeper than that on Trevor, I also think Trevor is a metaphor, built to facilitate every open-world GTA players' modern GTA power-fantasy, too - to do crazy, bad, reckless, and destructive stuff...without much of a care of the world, its inhabitants, and any sort of real estate/property - and this is why they (Rockstar) built him the way they did.
They have to, more so than anything, facilitate the story and things have to fit for the characters for why they are the way they are. Whether you feel what they did is worth buying into or not, that's another story entirely.
I think Trevor was purposely made to NOT be like-able. Heck, Michael too, for that matter - especially since he represents the American Dream...totally gone wrong. He had and current has everything in a material sense (money, cars, clothes mansion), but everything else...is a mess in his life (the situation w/ his wife and kids); hence the mid-life crisis.
There are reasons for all of this mess, so...whether you feel it's earned or not from the reasons, feels done before, feels cliches, or whatever - you'd need to play the game & its main missions to realize why they are the way they are; and then decide if you actually buy into what the game's selling here and their reasons & devices to try to execute this.
You have to also keep in mind - there are 3 leads, not 1. Out of the 3 leads, Franklin's probably the most like-able one of the crew.
Niko from GTA4 is very like-able and often says he wishes he didn't do the things he did, but still does them anyways and still does anything to try to reach the American Dream - but heck, he's certainly no saint either. Most GTA characters, to be honest, are not saints and it can be a roll of the dice on if they're like-able or not.
I certainly didn't find Vercetti that like-able (just like Michael in GTA5) - but given that he wasn't a blank slate like Claude (from GTA3), I certainly enjoyed them giving Vercetti some actual character, story, plot, and stuff...and that often was not seen from action games and open-world games that we often didn't see back in that era. And oh, Ray Liotta was awesome as a voice-actor in this role.