Oracle is a fine enough database (it really is), but it costs an exceptional amount of money and (I haven't touched it in a long time so I may be out of date on this, but I don't think I am) the developer tool experience is not great. Oracle SQL Developer is ugly and slow compared to SQL Server Management Studio. Basically, if you've used both Oracle and SQL Server you can tell which company had their CEO on stage shouting "developers developers developers" and which is run by the lawnmower.
There is another argument for or against adoption of Oracle and that is a basic business argument. Oracle is expensive and their virtualization costs are well above Microsoft.
Not the OP, but licensing comes to mind. MSSQL licensing and Windows Server licensing are a pain, especially in virtualized environments. But Oracle? The word predatory - complete with claws and fangs - comes to mind.