Welp, after another few rounds of deathmatch, I have some more info to bring to light. I, too, was concerned about the ADS encouraging camping, but there is an attachment - a special grip - you can unlock for each weapon that accelerates aiming. Thus, this isn't as much of a problem as I'd expected.
The killstreak reward system is definitely more simplistic than in mw3, and as I suspected previously, killstreaks remain less of a factor. Actually, they're called "score streaks" now or something like that, because they are activated once you reach a certain point total, not a certain number of kills., Fortunately, the point thresholds are sufficiently high that I have yet to even see some of the higher level rewards be deployed, which I view as a good thing because nothing is more frustrating than being dropped into a game in which the other team has 5 choppers and a blackbird up.
One thing that's different now is that you can activate more than one perk in each of the 3 slots, but in order to do so, you have to sacrifice one scorestreak reward, a secondary weapon/grenade, or an attachment. That is to say, there's a finite number of slots in your total loadout, and your can have more or less of each "type" of item or skill depending on your preferences. For instance, I dropped my pistol and my second tactical grenade so I could have 4 totals perks and 2 weapons attachments.
