Integration with all business processes, standard features, flexibility in configuration, full scalability.
Integrating Information systems between different business processes allows in my opinion the increase of efficiency in the organization. This is because data coming from HR is directly available to other processes. Extra HR (imagine Posting of Travel Expenses, Reports on Subordinates, Hours posting to WBS Elements or different Cost Centers, Employee's Master Data as Vendors or Customers of the Company etc.)
Room for Improvement:
Graphic interface and usability for end users.
SAP is not a last generation system. Users experience the use of the system as it was in 1998. I started working then and nothing has changed until now. Nowadays, people are used to web interfaces, user-friendly screens and rapid deployment functionalities. A different way of using the system in my opinion could avoid the thought that this system is not up-to-date.
Use of Solution:
Some during the first years, but nothing blocking.
There could be cases where the first configuration is not done in the most perfect way, in these cases some issues arise.
I managed very different kinds of projects. The product can be configured in lots of ways, everything depends on the customer and their desired processes to be designed.
Don't think it will be costless or effortless.
Disclosure: I am a real user, and this review is based on my own experience and opinions.