Depends on the game and the method of unlock, but I generally lean more in favor of having everything unlocked from the start than not.
In the case of fighting games, it's fine if there are unlockable characters for the sake of people who enjoy doing that, but if that's a method a fighting game chooses, if only for the sake of TO's and the like and making their lives easier (while also giving a nice choice to those who just want to get right into the action with their favorite characters), there should be some "cheat code" or other hidden option or something for people to bypass (and which isn't just throwing more money at the game or anything like that).
On the other hand, for something like say Mario Kart, it depends on the implementation and how it's handled. Like, something like the traditional method of unlocking characters through completing Grand Prix cups against AI racers sucks and is completely unsatisfying, because you're just racing AI, and while dealing with all the nonsense luck-based item might be fine when you're playing against actual human players and you can all laugh at each other, it's kind of a different thing entirely when it's just the CPU and you. On the other hand, changing to a more Smash-based system of unlocks, where there are multiple different methods of unlocking characters or something to that effect, that would be something I'd be more cool with.
I just don't find the Grand Prix stuff satisfying in Mario Kart, and having to win 150cc cups and deal with AI on that level and either somehow manage to beat the odds and somehow manage not to get unlucky at any point during that, or otherwise grind so much at the game and become so good at it that bad luck doesn't really matter, neither of those are very satisfying and what I'd consider fun ways of unlocking those characters at all, since it's all against AIs on top of it all. But while I would probably just prefer for all the characters themselves to be unlocked by default personally and keep the unlockable stuff to vehicle parts myself, if the unlockable characters were handled a similar way in Mario Kart to how said parts are handled, that would be something I'd be more okay with.
So when it comes to that kinda game, it definitely is much more about the method of unlock than anything to me I guess.