I think I am qualified to write this answer. I am a computer science graduate and have worked with two PSUs so far. I will be writing this answer based on my experiences in these organisations .
Your role largely depends on the kind of PSU you join. You will not be welcomed with many development related jobs as there hardly are any. Most of development jobs are outsourced so your role is limited to that of maintenance. You could be asked to work with marketing team or HR in case of manpower shortage.
Job satisfaction is minimal if you are really a career-oriented person. If you do not keep abreast of latest developments in your field you will be left far behind in the rat race in case you plan to switch jobs to private in the future. PSUs do not adapt to new technologies as fast as private sector. So there could be stagnation in your career a few years from now if you do not keep yourself aware of your field .
I have found people from IT field coming to PSU and they find this better in many aspects including pay, job security and peace of mind. Finally it boils down to what you expect from your job and your life.
Hope I cleared some of queries in general.