Oberon by itself is good for games.
Modular architecture is better then OOP for as big systems as a game engine is.
Well-tought and strict language is also advantage - or do you like buggy games? It's a norm novadays.
Typical Oberon program is a set of modules for a host environment (e.g. BlackBox). In conjunction with the reflection system it's really powerful. No need in scripting system - just write a module and use efficient, fully-featured Oberon for scripting purposes.

Text attributes in BlackBox are often used to highlight semantics (manually), not syntax. And possiblity to insert a picture into source code is also a useful one (why I can't do this in Delphi or VS??).

Garbage collector is also very useful in most cases. If you want to manage memory by hands - just take a large piece of memory and manage it manually.
But existance of Active Oberon-based real time OS BlueBottle tells us that there is no need in manual memory management.

Concerning libraries - it's possible to work with COM objects from a BlackBox application.
For games even 3D-math library is often written from scratch. Nevertheless, there are libraries for Oberon:
http://www.zinnamturm.de/

Disadvantages (or why I still not at Oberon):
* very small community - recently the interest to Oberon is incresing but it's still small
* lack of ideal compilers - BlackBox is good but the code it generating is not very fast. Code generated by XDS is fast, but XDS doesn't have an IDE, not open source etc.
* lack of libraries