D5500 doesn't have the viewfinder to manually focus easily(or well).
It's main issue is the use of a pentamirror instead of pentaprism(brighter), and the fact that the ground glass, or focus matte, is optimised for f/5.6 aperture lenses, hence DOF.
(hopefully in simple terms) what this means is that while your lens may well be f/2.8, you don't literally see an f/2.8 DOF, you only see a DOF(through the viewfinder) of f/5.6.
In terms of manually focusing, this makes it hard to see. You get a green dot/rangefinder feature, but their not particularly accurate.
You could get a more optimised focusing matte, easily changeable .. but easily damaged in the process too! .. cost is about $100-ish give or take a few for exchange rates.
While it's easy to think if it's a simple matter of just changing the focus matte screen, then why don't the manufacturers just do it!
Answer is that as they make them more coarse, and therefore easier to view the DOF of an f/2.8 lens, the image through the screen(the aerial image) gets increasingly darker!
Tell 'im he's dreaming!
From what I can make out(I've yet to see any direct comparisons between the two lenses) the edges of the frame in the G2 do look a bit better than the G1 version.
I doubt bokeh will be better(by any significant margin), and so far from what I've gathered CA looks a little worse on the G2(I think).
I think there's enough sharpness in the G2 overall compared to the USD(or G1 version) .. but I wouldn't use that as a basis for buying it over the G1 version.
Also note that sharpness across the frame sometimes is 'over rated'. Unless your doing planning on doing panoramas, I'm thinking it'll never come into play for you.
if you do have plans to do panoramas, then for sure you'd take edge sharpness into consideration.
For me the main reason for choosing the G2 is simply the dock.
And not only for the geek factor of it, nor the ability to tweak it to taste in whatever way it allows .. but for future compatibilty, with zero hassle factor.
I'm sure at some point in the future Nikon will try hard(er) to make thirdparty lenses incomaptible .. they have till now, and I think will continue this line of thinking into the future.
So some lenses may become 'incompatible' with future camera bodies in some way. No one knows which way, or if at all, but usually a firmware fix does the trick .. the USB dock(for me) is this insurance.
And I hate the process of taking gear to a repairer to get it sorted .. when a firmware fix is so simple to do in the luxury of your own home, having a decent quality cuppa to boot.
And to be sure, because you mention bokeh as a quality that's important to you, then if this is the case, then edge sharpness is(or will become) less concerning.
Don't get me wrong here, you can and could use the lens for both properties, but I tend to target one aspect over another. Great to have both properties if it's possible tho.
When I had my play with the G1 version, and ended up with the Tammy 24-70 instead, I updated to the 24-70 from my old Tamron 28-75/2.8. The lens worked really well, blurred very nicely and made nice 'people' images with that well rounded blur, but for landscape panoramas, it's edges were not 'so nice' .. sharpness for me wasn't the problem, vignetting was .. and this is coming from a habitual vignetter!.
When you do panos in multiple stitch efforts, you don't want vignetting.
Usually stopping down to f/8 is enough to remove it enough so that it's not a problem .. not with the 28-75 tho .. I tried f/11 and still had just enough vignetting that it drove me to skip the 70-200 and get it instead.
There's not really a lot of info around on the G2 lens, some here some there, but not a whole heap.
I was looking at LensRentals blog post about it. looks exceptional in terms of IQ. And as the salesman said, across the whole frame. There's no directly comparable data on the older version of the lens tho. That data is more traditional MTF data, so I've kind'a extrapolated it's data and estimated the difference. Hard to know for sure tho how much different they'd be side by side tho.