There are only a few cons that are static, but all organizations can and must improve. Historically low turnover so new job opportunities are slow to develop - but that is changing. Historically a culture of low performance expectations and often times inadequate ways to measure performance. That too is changing in some departments that have or are developing new business technologies to measure productivity. But managements frequent failures to implement technologies that deliver their intended business results over the long haul, and a lack of will to confront poor performing individuals who may be long time friends, could mean working with peers having completely different contribution levels but similar pay/rewards.
Utilities, by design, are not risk takers as they are typically not rewarded for taking risk and punished in earnings when initiatives fail. For this reason, this company is not one where risk is well tolerated, and this permeates down to you, the work of the individual contributor. Ambitious undertakings of highly complex issues are certainly undertaken, but for the typical employee, this kind of environment frequently better rewards individuals who take the safe and predictable route and produce no surprises over individuals who push hard and deliver on a more risk laden project. So if you are one who wants to push the envelope and take some risks to achieve beyond what is often considered mediocre in truly competitive environments, you may not get many opportunities here, and if you do and are successful, there is not the kind of reward you might typically expect for the extra efforts.