Pros
Overall, I'd definitely recommend working at RES. I think most people you'd meet there are really knowledgeable and would be willing to share their knowledge with others. The work is varied and interesting and there are opportunities to learn and grow within the business. I'd say that salaries are also in line with the market rate.
Cons
Depending on the team, you may be required to work quite long hours. Most weeks I'd do 50-60 hrs which put strain on my family. This has not been the case when I joined another developer - the workload has been manageable and I very rarely even turn on my laptop on weekends which is definitely a nice change. The overall company culture is good but you'd find an odd team where people do not feel empowered to speak up which in my view is largely due to certain individuals in the team. The issue has been addressed by the management though which is a good sign overall. Finally, the biggest issue that I have observed over the past couple of years has been a shift in strategy. RES has increasingly started selling their projects at earlier stages. Since the development pipeline can't keep up with the increased demand in terms of budget requirements, it is difficult to find attractive, well progressed projects. Not sure if there's a way to fix this - projects take time to develop, meanwhile, the development arm of the business is expected to deliver a steady revenue stream every year. With the recent M&A activity it is clear that RES is trying to shift their focus towards support services. Hope this approach works in the long term.