This is a special, something beyond the main story, and as such it must be viewed.
There are not revelations, no secrets, no nothing. Just pure enjoyment. If you can watch it like that, it's almost impossible not to like it.
It's hard to analyse a special as a whole, specially when there's a main anime behind it, but...
The story itself is quite simple and you don't have to be a veteran anime viewer to predict how it's going to end, but again, it's rather how i'ts told than what's told that meke the special so enjoyable.
Same art as the main series, which is quite good, there are some nice details and there's no abuse of CGI for the street basketball game. Easy to watch.
Again, it doesn't go or try to go away from the main series, GRANRODEO gives KnB a nice touch; the voices are the same, which are quite good, and the BGM helps and goes well with the story.
Kuroko, Kagami, Aomine, etc. They are the same of the anime, but changed after all that's happened, and the change is well shown, the are no strange things.
Pure enjoyment. A special to watch, enjoy and go out for a buguer after it. It will probably leave you with a smile, and that's great in every way.
I'd highly reccomend the Saikou no Present Desu to any KnB fan or viewer who has finished the anime.