Is it a specific mechanic/thing or just being happy with the games you have and 5E not being a good enough upgrade to consider buying it?
I am generally positive about buying and playing 5e. But I do have my dealbreakers!
It's not about specific issues. I have them too (the Human race, skewed saving throws, way too many +1 magic weapons, dishomogeneous level placement of subclasses...) but there's nothing that individually would be a deal-breaker.
These can be the real dealbreakers for me:
- a general feeling that the game is half-finished (all those specific issues above left unsolved would contribute to this, because each of them divides people into a group that hates them like that, and another group that doesn't care or is merely OK; no action against those issue means the designers don't care about the gamers who care)
- too high complexity even when choosing all the lowest-complexity option; the edition must be casual-gamers friendly or I just won't have a group to play it with
- bad editing and publishing work, meaning that the books are full of errata or have abysmal organization, making them a pain to play with
- wrong choice of artwork style (e.g. manga, splatter, sexist, pulp or too violent): I really need to be inspired to spend my time DMing, and artwork is what can really inspire me or turn me down