There are numerous photo sharing websites out there. Some have the more serious photographer in mind. Here are my favourite picks at the moment.
Gurushots is a very nice website with associated apps for android and iphone (although I could not find one for iPad). Emphasis is on competitions and rankings. It’s fun to play and although they encourage you to buy things it’s not necessary and easy to avoid. Check it out here. Link opens in a new tab and I have to disclose that I get a few trinkets that help me play the competitions.
Viewbug is along a similar vein. They also run competitions, called challenges. You can earn badges with a bit more variety than Gurushots. It looks like you can create a challenge yourself straight away, unlike Gurushots. Viewbug is available on the Apple app store but not on Google Play store.
Playing competitions gets you thinking about your own images and your fellow competitors. Somewhat addictive but thoroughly enjoyable.