Recs.
Updated
Specs
Pros
Pro Plenty of useful features - cache, cron triggers, task-queues, etc.
GAE offers a whole lot of features that can become quite handy once your app starts growing in scale and complexity; a built-in cache service, datastore, fairly advanced path mapping, static hosting and auth configurations, remote data dump features, etc.
Pro Seamless integration with Google services
App Engine natively takes care of authentication and other hectic aspects when it comes to accessing other Google services; you can simply import the SDK modules and do your stuff (e.g. sending out an email, saving a Datastore entry) with one-liners.
Pro Easy to use
Google App Engine is very easy to use. All you need to do is install the SDK (which in itself is easy as well, and the documentation is very heplful) and run the command needed depending on the type of project to deploy it.
For example, to deploy a golang application, you run golang deploy inside the project folder and it will be automatically deployed.