I have used a camelback/hydration pack on many rides and liked it. The one I have is a small backpack really so there is space for wallet, tools, etc so I can get ride of the saddlebag.
Upsides: lots of water capacity. Less time with your hands off the bars for a drink. More aero.
Downsides: weight on your back might not always be agreeable, I solved this by favoring to drink from the camelback first over water bottles. The water flow isn't quite the same as a water bottle. Favor more small sips with a hydration pack but if you want more water at once, grab the water bottle. Can't/shouldn't be used with anything but straight water according to the labeling on mine. It's very difficult to get the bladder fully dry and anything that can cause something to grow in there is iffy.