I'll be honest, I really didn't like Ruby or Sapphire, so I really only got AS for competitive reasons (I can only imagine that the genies and Lati@s will be VGC legal for next season), and in fact I chose my version based on which had the better legendaries from a competitive point of view. I am also only 4 gyms into the game so far (end of semester is always a nightmare), so my opinions should probably be taken with a grain of salt, but here are some of my impressions on the game.
I haven't gotten to the massive water parts yet, but I hear sharpeedo makes them a lot more bearable because he moves twice as fast as other surfing pokes.
New Mauville ridiculous and horrible.
Game looks pretty, but so did X/Y so that's not really a surprise.
Hear you can get a non-event Deoxys in post game, that's a big plus.
They removed the pokeblock creation game. This is unacceptable.
Secret bases are cool.
Game is even more linear than I remember so far. I know this seems like a petty complaint because most pokemon games are, but I still love being able to do the gyms and stuff out of order in R/B and S/G. In this game it feels like I'm being forced from one town to another
The villain teams are just as nonsensical and dumb as before.
The removal of trainer customization from X/Y is frankly unacceptable.
In general I feel my complaints against the original R/S will still hold up, but if you are the kind who has nostalgia for them, game should be fine for you.