- Good reporting features: TM1 (for planning, plans vs actuals analysis, what-if analysis) and SPSS (for predictive analysis and other type of analytics).
- Integration capabilities: broad enterprise integration feature set, useful APIs and SDKs.
Self-service analysis features have improved a lot, even with new subversions of version 10, but I feel business users can't really utilize these features as they are not too intuitive and they easily find themselves lost among Cognos Studios. Query Studio is easy to use, but you can easily reach its limits. Analysis Studio is for OLAP analysis and it's quite easy to use, but OLAP needs a predefined multi-dimensional data source. Report Studio has lots of power, but it's too complex for a business analyst to use. Cognos Workspace aims to provide some self-service capabilities, but it's good for dashboarding only. Cognos Insight has been designed to close this gap, but it's quite a new solution; therefore, it lacks some complex analysis features.
Another area for improvement is error messaging. When an error occurs, the user has two options: the user gets a message that an error occurred, logged and please contact the admin, OR you get a long Java exception that you don't understand if you are not both a Java developer and a Cognos architecture expert (so there is a big chance that you will never know why the error happened).
I have been using Cognos BI version 10 since 2011, and previous versions since 2003.
Stability depends on many things, e.g., the quality of the Cognos model, the stability of the data source, the stability of the Cognos server environment, the stability of the network between the server and client application, the amount of data in the report/analysis, etc. Stability can be increased with a good initial setup and a thorough stability test of the Cognos BI environment. But it might happen that a user receives a strange and unidentifiable error message due to stability issues.
Scalability depends on the scalability of the source database system and the BI system, as well. Cognos BI can be scaled well, but the scalability of the source database system is more important in most cases, especially when a huge amount of data should be reported/analysed.
Technical support has two levels: first-level support is provided by an IBM support partner. So the quality of the first level of support depends on the experience and the quality of service of the support partner. Second-level support provided by IBM can be slow, especially when a competent IBM technical expert can't be found in your country.
I have seen some cases when an existing BI solution has been replaced by Cognos. It had various reasons but in most of the cases, the existing BI solution was outdated or the customer was disappointed with the existing BI product or simply the IBM salesperson performed well.
The complexity of the initial setup depends on the product variant itself (for. ex., Cognos has an Express version, which can be set up really easy), and it depends on the planned BI architecture as well. So it can be really easy and it can be really complex, too.
Cognos BI has role-based licensing, so think well about which BI role you really need, and whether you should buy user- or CPU-based licences.
I always advise to use the right product to your specific needs, and evaluate some other options as well. Cognos BI can be a good fit for you in one case, but it might not be the best solution in another one.
Look for a good implementation expert who can help you make it a success. And don't spare on trainings; it's a complex, enterprise BI product.