Fate 2.0 is hands down my group's favorite system. When Fate Core came out we immediately took it up with enthusiasm but ended up going back to 2.0 because of Fate Core's relative shortcomings. We now use it more or less exclusively for a homebrewed JSR (John's Scion Resources) inspired Scions remake. Here's why:
Fate Core is Unmitigatedly Narrative
Our play group is diverse and we do not find the same things fun in RPGs, nor do we like to play the same way. We don't have a shared playstyle, except in that most of us (the ones we regularly let have GM powers anyways) work to accommodate our diversity of playstyles. Fate 2.0 is the only published system we have played so far that actively supports this kind of group, by providing multiple different ways to purchase effects in the Game.
Aspects in Fate 2.0 are character-focused and provide a method for players to establish sweeping character-based control in a game. Aspects establish who a character is and allow that to shape play in a meaningful way independent of narrative, simulationist, or other influences. Relying primarily on your aspects allows you to build a character based around a certain 'feel' and have that feel fairly represented in the actualization of your character within the play-space.
In Fate Core, aspects require fate-point invocations to exist, and act more like labels than character traits; they are only carried out within the play-structure when it is narratively convenient. This is different than only being carried out when it is useful to the character-- Fate Core certainly encourages the use of 'compels'-- but compels are encouraged only when they would be narratively interesting.
Skill selections in Fate 2.0 are also somewhat character-focused, but appeal more to those who employ a detailed, simulationist approach to play. The ability to approach a small set of player-chosen activities with extreme detail and have that attention to detail rewarded within the play structure, while permitting with penalty abstraction of unimportant areas, is engaging and rewarding for this kind of player, without being an obstruction to others' enjoyment.
In Fate Core, skills are narrative tools. Rather than being able to use a blacksmithing skill to blacksmith, you use a blacksmithing skill to progress the narrative in a certain limited set of ways (you can pay with stunts to let you evolve the narrative in more ways), based on the possible action types. Furthermore, rather than player-generated skills, the skills are by default GM-generated in a skill list (this was merely one of several optional approaches in 2.0). This change to the skill system effectively renders simulationist play in Fate Core completely infeasible.
Balancing Extra-pyramid skill-point subsytems, unusual skill configurations, and explicit levels of specificity in 2.0 appeals to the gamist player, who has space and a framework in which to weigh mechanical options against each other within the context of a single character. Gamist play in 2.0 is entirely possible and does not disrupt the game if done well.
In Fate Core gamist play is explicitly shunned and looked down upon as some kind of lesser playstyle by the community at large and to a lesser extent the actual system. A common mantra is that trying to apply and interact with the mechanics outside of a narrative is the wrong way to play Fate Core, which I would agree with; the mechanics are exclusively narrative so outside a narrative there's nothing to really grapple with.
The interactions in FATE 2.0 allow players to approach play in a plethora of fundamentally different ways within the spectrum of playstyles the game's play-space conceptualizes. Furthermore, the system's backbone is extremely unstable in playstyle and can easily be resolved to allow additional, different spectrums of play approaches and/or to bias itself towards certain approaches in a given campaign. Fate Core is very much like a well-built and fundamentally better exclusively narrative campaign of FATE 2.0. In FATE 2.0, you can't really remove the multi-playstyle nature of the system entirely, even as a single player, and so all the players have to engage on at least in minor level with most of the ways the group is approaching the game in a given campaign. Fate Core helps focus the game on a single kind of play, which makes the system worse for situations where you want to have a different kind of play.
So Fate Core is generally less good than FATE 2.0 for:
- Simulationist players
- Equipment-focused Survival Campaigns and other detail-oriented simulationist games
- Character-focused players
- Slice-of-Life Campaigns and other Literary-Realism-like character-based games
- Gamist players
- Narrative-less Arena Fighting and other classic player-competition-based games.
- ...And any other player or game, who or which is not, broadly speaking, narrative.
Fate Core Tells Only a Particular Family of Narratives
Fate characters are proactive, competent, and dramatic
Furthermore, though this is unstated in the above quote, Fate Core characters are narratively dramatic and work as a party, and Fate Players can change, ignore, or add fundamental aspects of the narrative in-game via fate points and Create an Advantage actions.
This further eliminates:
- Most Administratively and Logistically focused players and games (you can do logistic narratives, but a narratively dramatic character makes this harder than it needs to be and shoehorns it out of most of the common tropes for the genre)
- Many political games
- Psychological Horror
- Much Gothic Horror
- Multilayered Longform Literature-like campaigns, and other games that require heavy handed railroading
- Philosophical Investigations
There is some overlap here with the previous list, in that both factors often contribute and it's hard to say which one specifically is the one that does the kind of play in the most.
Fate Core caters to a particular subset of narrative play. If you and your group want to play that way exclusively, then there's little reason not to use the system exclusively. If you want to play with a different kind of narrative, you can probably use the system with modification to accomplish that, though you may be better off with a different system that does the thing better. If you want to let players who have non-narrative playstyles participate and have fun, minorly altering the base system of Fate Core will not be be a good approach and you will want to use a different system.
Please note that while this answer is critical of Fate Core, the system does have many merits, and does what it does quite well. Superhero fiction, mythology-inspired heroics, narrative-focused adventure-y Medieval Fantasy, etc. all work very well in it. Superhero fiction in particular it does much better than FATE 2.0.
And that's just Fate Core v.s. Fate 2.0
There are just so many really, really good RPG systems and subsystems out there. Even for things Fate Core is good at, what we really have to be considering isn't if it works well but if it works the best. Even when it's good, there might be something better, and if it's not too much trouble for your group to find and learn the better system that's an excellent reason to not use Fate Core. Maybe you even like learning new systems. That isn't to say only the best system for a thing is any good, or that not trying new systems when you've found one that works is bad, per se, just that having an even better system is a good reason not to use Fate Core.
I mean, that's the whole idea behind FAE, right? To be even better for a subset of the people who would like Fate Core.