I played Civ5 for far too many hours last night, and did have a blast, but I am a little disappointed with a couple of aspects that feel
streamlined. Things I don't like off the top of my head:
1. Can't trade science technologies. (this feels the worst)
2. Hexes isn't something I dislike... it is just something I don't get. It doesn't feel like as big an advantage as was marketed.
3. I can't adjust the tax and science rates? WTF?
4. Where are my towns and cottages? (though this isn't a huge loss).
5. The game feels quite a bit easier to me, though that just probably means I have to play at a higher difficulty.
6. The science tree feels very much out of sync with the appropriate time period.
7. I really want the espionage stuff back. I bet it will be done for an expansion, like before.
OK here are the changes I like.
1. Not being able to stack units isn't something I *like*, but it isn't so bad. It does definitely add a tactical aspect to it.
2. Towns being able to defend themselves etc, is pretty freakin' awesome.
3. The game looks good.
4. The whole adviser stuff has been handled quite well. Still doesn't hold a candle to Civ3, when all the advisers were in FMV, with their outfits changing with the period, and the entertainment adviser was Elvis!

5. The respective civilization histories have been presented in an excellent manner. I started with the A-RAB empire, and it's history was presented truthfully and respectfully.
6. Combat information etc is also quite well done.
7. World Leaders and stuff speak in their own languages and stuff, and are presented quite well.
So, I am looking at my list, and I note that almost all the positive changes have to do with presentation, and the negative changes have to do with streamlining.
That's probably not too good. Civ has always been pretty complex, and has still sold well. Still enjoying the game though.
edit:
The game has also crashed for me, a LOT. Almost always when I am saving or loading. Performance otherwise has been excellent though on my aging rig.
edit: Just pasted my entire post from PCG, and am editing some stuff out.