I downloaded it and so did my boyfriend and our housemates. It's still having a lot of server overload issues, and it took over a day for me to be able to do anything. Still getting kicked out sometimes, but it seems to be stabilizing some. I haven't played it enough to really have too much of an opinion on it, but so far it seems alright. I think it needs more social/peer-to-peer functions soon to keep it going (why can you not trade Pokemon with other users?), or else it's going to fall off the radar after the novelty dies the way Miitomo did earlier this year.
Edit: Looks like it's blown up on social networks that on iOS, if you sign into Pokemon Go with your Google account, which I bet many users did, myself included, the app/Niantic has full access to the Google account. Not cool, guys. That is a HUGE privacy problem and could be a hacker's paradise, especially now that it's gotten out there. Guess who just revoked access. Fix it, Niantic. Now. No excuse for that.
http://kotaku.com/pokemon-go-gets-full- ... 1783467458Edit 2: Well, at least they were quick on the turnaround and both Niantic and Google are working on a fix, as that level of access was never intended. I bet Google can just flip a switch on the back end to lower its access permissions, but that will be invisible to most users. Niantic should probably issue an update to the app that fixes the permissions it requests. I may sign back in just to see if Google did a back end fix. I'll feel okay (if ever diligent on my google account) playing it again when I don't see it listed as having full access on my Google security settings.