In one of the biggest changes to paid search advertising since the dawn of the Internet, Google Inc. (NASDAQ:GOOG) on Monday will switch over all of its AdWords campaigns to “Enhanced Campaigns,” but not everyone is feeling enhanced.

The changes, first announced in February, are meant to simplify how AdWords advertisers manage their campaigns across various platforms. In a blog post at the time, Google AdWords officials pitched it this way:

“With enhanced campaigns, instead of having to cobble together and compare several separate campaigns, reports and ad extensions to do this, the pizza restaurant can easily manage all of this in one single place. Enhanced campaigns help you reach people with the right ads, based on their context, like location, time of day and device type, across all devices without having to set up and manage several separate campaigns.”

Google has been strongly encouraging its advertisers to upgrade their AdWords campaigns before the July 22 deadline. Those that don’t will find that the AdWords system will upgrade them automatically, using default settings.

But many online advertisers have been dreading the mandatory changeover, which they say will give them less control over their AdWords campaigns.

“[I]f you are an expert AdWords advertiser, you probably want to control your mobile, smart phone, tablet, and desktop campaigns differently,” wrote Barry Schwartz, a writer for Search Engine Roundtable, shortly after the announcement. “You probably want to bid different, show ads differently and not have Google make those decisions for you.”

Still other advertisers seem to be unclear on what the changeover to Enhanced Campaigns even means. A survey of 750 brand-side marketers performed by Econsultancy found that 56 percent were unclear how the change would affect their search marketing activities. Only 29 percent thought the switch would have a positive impact on their campaigns.

In a conference call on Thursday for Google’s second-quarter earnings, CEO Larry Page noted that advertisers had already upgraded 6 million campaigns -- almost 75 percent of all active campaigns. However, that leaves 2 million campaigns that still need to be upgraded before Monday’s deadline.

Google’s earnings fell short of analysts’ estimates. The company reported that cost-per-click, or CPC, decreased about 6 percent from Q2 2012, and it declined 2 percent from Q1 2013. The numbers are curious since the ushering in of Enhanced Campaigns is widely believed to be an effort by Google to raise CPCs.   

In a blog post Thursday, Larry Kim, founder and chief technology officer of WordStream, suggested several possible theories for the CPC decline, one of which is the increasing use of mobile devices. The shift from desktops to mobile poses a challenge to Google’s traditional advertising model, as mobile devices, with their smaller screens, have proved more difficult to monetize than desktops. 

“For various reasons mobile clicks have historically been cheaper, and if the growth of mobile search is outpacing the growth in more expensive desktop clicks, it has the effect of dragging down the weighted average of the two,” Kim wrote.

Google, for its part, has posted tips and recommendations for advertisers that still haven’t upgraded their campaigns. You can find those here.