Is it unfair to ask this?
Yes, because our opinion can change with next packet. But who cares? Go ahead
Is 5th ed doing the things your preferred edition(s) did better?
My favourite edition is 3.0. It's main strength was flexibility (especially in character creation), and I think 5e has about the same, and it looks like it's getting even more and extend that flexibility also to the whole game.
Is it addressing the things you saw as problematic?
Problematic in 3.0 (and 3.5, and PF...) is that you need "system mastery" to enjoy the game. I used to like that, but now I just don't have time anymore to keep up with it, and its long DM's preparation time and slow pace of a campaign due to long fights, and fiddly bits in all situations... 5e is doing a fantastic job for the DM because it is indeed simpler to prepare and faster to run. It's however still a lot complicated for players, but we haven't yet got a clear idea on how "Basic" will handle that.
There are problematic things in other editions. Older editions aren't flexible enough, 5e is. 4e isn't traditional enough (for my tastes, IOW didn't feel enough like I was playing D&D), and 5e has a few elements that unfortunately are still harming the sacred cows, but at least it's trying as much as possible to offer alternatives.
Generally speaking, I want
simplicity,
flexibility and
tradition. Any lack of these beyond a certain threshold, and I have a problem: if it's not simple I just can't afford to play it; if it's not flexible I don't see myself playing it more than a bunch of evenings; if it's not traditional then I have no reason to prefer it over any other RPG. 5e is quite ok with the 1st and 3ed, and definitely doing a good job with the 2nd.
Also, to what degree is it shaping up to unite disparate edition bases?
I see a lot of principles of 3e in 5e, to the point that I think a 3e fan can have few reasons against 5e except money (i.e. if they spent a lot on 3e books they may just not want to spend them again on 5e).
I didn't really play 4e except for a few evenings, so I totally missed its development through the years. From what I think I know, 5e is slowly incorporating more and more 4e ideas. Whether this is enough to capture 4e fans I have no idea. Whether this it already too much to alienate 3e fans who also hated 4e (like me), well I think not yet, but occasionally I do feel like I'm starting to be a bit pissedoff...
Does it yet look like it will be playstyle and conversion friendly?
Yes. Presumably it won't be ever able to support every conceivable playstyle, but they are trying indeed to be inclusive, and at the moment it quite is. (See next about converting)
Is it heading in a direction that will make older modules and characters easily portable?
I really don't know... At the moment I would say no, at least not any easier than previous editions switches.
5e characters might be close enough to 3e or 4e characters of the same level. But bounded accuracy and damage bloat means that clearly you can't take a 3e or 4e PC of level N and put it into a 5e game for a party of level N, because it will have much larger combat stats and lower damage output. Maybe it would even out after all... but generally speaking, I think you'd have to convert it, and same for modules, you'd better just use the 5e versions of monsters (after checking that each encounter is still within the encounter building budget).
edit: forgot to mention that equipment will be a significant conversion problem, at least from 3e which assumed wealth-by-level; if the whole 3e party of PC is converted to 5e then almost no problem (except with items of large number of +s), but if just some PCs are converted to join a 5e party then it might be necessary to totally replace their equipment