First, the servers have been going up and down like a yoyo, which despite its unprecedented success should never have happened more than once.
Second the app on iOS crashes every few minutes - I've never seen a more buggy app. Using Unity no less. It's not due to some weird edge case, it's constant... log the damn errors and make sure it doesn't happen again. It's Monday, I should have had an update from the App Store by now, but nope.
Third, there's apparently no caching (which might explain their server problems). Every time the app starts (or more likely crashes and restarts), it hits the server to download all the local POI info again from scratch. God help you if you're in a spot with bad connectivity.
Fourth, what is it doing do drain the battery so badly?? I've driven for a couple hours with maps apps running without killing my device. It must have zero logic in the app to manage power drain because it'll kill my iPhone in an hour easily.
This game owes its success 100% to the popularity of Pokemon and nothing else, the app would never had any success if it had to stand on its own merits. As it is, Niantic is doing its utmost to kill the franchise with their ineptitude.