According to Microsoft's blog post, the new tiers offer a stronger uptime service level agreement (SLA) at 99.95 percent, plus support for larger database sizes (up to 500 GB) for less money.
Microsoft's descriptions of the three new tiers:
1. Basic: Designed for applications with a light transactional workload. Performance objectives for Basic provide a predictable hourly transaction rate. 2. Standard: Standard is the go-to option for getting started with cloud-designed business applications. It offers mid-level performance and business continuity features. Performance objectives for Standard deliver predictable per minute transaction rates. 3. Premium: Designed for mission-critical databases, Premium offers the highest performance levels and access to advanced business continuity features. Performance objectives for Premium deliver predictable per second transaction rates.
Here's Microsoft's pricing chart for the new tiers.