I hate to throw around the term "dumbed down" with Civ V, but actually.. it's truthful, at least partially.
I think Stethnorun wrote well, even though I say it was a bit biased and I don't agree with many things on it..

But what strikes me is that stuff you don't like are some of the things that make Civ IV more complex and rewarding for me. for example you wrote:
"It's funny you bring up maintenance. I always HATED that feature. It made colonizing other continents, especially, very unappealing. I was overjoyed when Civ 5 got rid of that penalty and made all cities alike, regardless of distance or landmass.
Just personal taste, but man is it nice to get rid of that nasty "I shouldn't be settling this far away" feeling in the back of my mind."
Again, another case of having more decisions and planning in Civ IV. Should I start my own colonial British Empire where the sun never sets, or will it cripple my economy like with Spanish Empire? Now that I have colonies, should I grant them independence?
That adds both to deepness and to the "feeling" (or roleplaying aspect as some call it), and personally Civ V needs more stuff like this.
There's some much cool little stuff in Civ IV that I can't even think of them all, and I think stuff like this adds to the liveliness of the world and the grand, epic feeling.
Colonies
Important part in the history of empires. Wasn't in Vanilla Civ IV but came with BTS I think.
Random events
I kind of understand why some people play with them off in Civ IV, but as I'm not a high score type player I think they add vast amounts of detail and realism to the world. One of the things I think that Civ V would profit from would be the return of these.
Resistance fighters
Just a small thing, but cool anyways. When you conquer a large enemy city, part of it's people spawn as resistance fighters or militia to battle your troops. I like it.
City rebellion
In Civ IV, if you have a conquered city and there's not enough garrisson, it suffers from rebellions and might be in danger of turning back to it's previous owner. If I recall right in Civ V you need just time to quench the disturbance.
Health
Again, why to take it off? I guess this is streamlining..
War weariness
Essential part of Civ for me, why NOT to have it? Demands more strategy and is also more rewarding in the sense of atmosphere. In Civ III I think the goverments and war weariness was done really well.
In Civ IV losing lots of units also adds to it, makes sense.
Army Maintenance in foreign campaigns
When Napoleon drag his SoD around Europe, he needed the gold to flow to sustain his
grande armeé, in Civ IV units take more maintenance when out of borders, as simple as that, and works fine.
Navies
There's been it's own topics for this, but when in start I though having embarkation in Civ V was nice, now I feel it's a bad case of streamlining and takes away the grand feeling of building your navy and thinking about what other projects to sacrifice when building the galleons or transports.
Here I didn't tackle the biggest topics of IV versus V in depth issues, but about many small details that add to the experience.
By the way,I play Civ IV in middle difficulty levels, and I haven't had any big problems with stacks of dooms, like having an enemy stack of 100 approaching me.
Instead of 1UPT I think it's obvious that something like ten units per tile would have been the right choice.