I personally didn't think it was bad. Also, I'm mostly annoyed because people keep talking about how linear it is while refusing to see that it's identical to 10 in that regard, at least until you beat 10. 10 was literally a hallway too
What most people don't recognise is that all the flaws in FF13 were present in the games that were widely accepted as being the best in the series. Until you get the Highwind, there's not much to do off the beaten path in FF7. It just feels much more open than it actually is because you move freely on the map. Doesn't change the basic linear path you're following, it just masks it. Same goes for the combat. You're still moving through a menu, choosing an attack/spell/whatever and selecting a target. You press the same buttons and perform the same actions, it just feels different, though I will admit you had more choice in FF7's materia system. But think about it. Final Fantasy was never really that open or that involved in the battles.
As for the 13 trilogy as a whole, it has its problems, I won't deny. But 13 is at least playable and indeed enjoyable despite some seriously questionable design choices, such as the 'party leader KO equals game over' which regularly leads to said game overs if enemies choose at random to use their instant-kill bullshit attacks on the party leader. 13-2's story is damn near incomprehensible, time travel is always a can of worms. But the gameplay was better refined. If a game had 13's story but 13-2's mechanics, it'd be a solid entry. Lightning returns was just hot sweaty garbage. The story was nonsensical and barely there until the end, the clock severely limited gameplay options, the levelling system was ridiculous, it just felt like a collection of loose ends thrown together. Sazh's whole quest line is just kinda there, it has no build-up, no previous investment, nothing. And then the game just up and throws a fight against God at you out of nowhere at the end when Lightning just decides to smack a deity up. I own it for the sake of a complete set, but I consider it by far one of the weakest games in my entire collection. And I own Sonic 2006.
The trilogy just got worse as it went on. There was no reason to even make it a trilogy to begin with. 13 holds up reasonably well on its own as a slightly below par FF main series title. But then it's not like the entire series was ever flawless to begin with. FF2 had major problems too, 3 was pretty forgettable. Honestly, the FF series has been in serious trouble ever since Hironobu Sakaguchi left to form Mistwalker. I've all but given up on it. I have serious doubts about 15, the FF7 remake being episodic already has me concerned that they'll cock it up. The series stopped being its own thing and started chasing whatever was 'in' at the time. It needs to start setting trends again instead of blindly following them for the sake of the casual gamer dollars.