Openshift, Red Hat and Fedora users community, opensource community.
Culture and ecosystem with hackatons and community events (conferences, seminars,webinars).
Most recent cutting edge opensource software and technologies.
Support and extensive documentation, educational resources.
Easy to implement and make experiments.
Highly extensible and scalable, Openshift apps can scale from single-page app to a large infrastructure or network, fully controlled monitored and orchestrated.
Minimal network latency for servers.
Openshift containers and cartridges and plenty of github repositories available with custom configurations for those containers / cartridges and apps.
Constantly providing new features and publishing newest tutorials.
Pricing for individual learning and experimenting and for professional projects and hosting.
Build for developers, developers and DevOps best friend.
Easily integrated in other cloud services and cloud providers.
Pre-built applications, ready to be deployed in minutes.
I think there are not many issues I can count which i dislike.
It can be complexity to build and scale custom apps, though OpenShift is not for plain users but for developers and professionals.
Sometimes hard to build a new application with experimental features, I need to build a new cartridge for that application first and I need to keep all manifest and config requirements.
I move almost all my development environments, mostly staging, outside of production to Openshift.
I make domains with demo.* and dev.* prefix at Openshift and provide "live" development environment for my customers and clients to observe work-in-progress.