To piggy back on what M20EPilot said, I know a few guys who went to Great Lakes because it seemed to be their best option at the time. They have all said that the flying is great, but pay is not so great. A friend of mine stayed at the company for 7 years and loved every minute of it, but left for better pay. I know several guys who went to Great Lakes and got hired straight into Frontier Airlines. I know a couple others who left Great Lakes and went on to fly jets at various part 135 companies and later move on to the majors. Your experience may vary.
I debated going there several times, but the reasons why I did not were:
1. no pay during training, and I couldn't afford that, but some people can afford that
2. 15 month contract (begins after training is complete). I knew that I would get to 1500 hours well before the 15 months and would want to fly somewhere else
3. I made more money flight instructing than I would have made at Great Lakes
4. High chance of PRIA event. I have a lot of friends who made it through the company successfully and I don't view myself as being behind the power curve on this one, but the idea of high attrition in a training program was a secondary factor for me.