I agree with Adams comments. The iFly 737 is great and in fact does some things better than the PMDG 737. It will further improve with the coming HD texture sets.
At first flying a FMS (Flight management system) can seem daunting but once you have the basics sorted you can be up and flying in no time.
Grab a java and go thru the manual and the tutorial. It is a very good place to start. This is not a "purchase, jump in and go" machine. There are many videos around that can guide you on the FMS and other aspects of operating the aircraft. The iFly forum is also a great place to go to and browse through past posts. Pay special attention to the use of the CDU (keypad) and the autopilot. Learn what the various modes are and what they do. Learn what the FMA's (Flight mode annunciations) that are displayed on your PFD mean. They tell you what the autopilot is doing or commanding the Flight director to display. Use the autopilot as much as you can to offload yourself. Remember that this is a 2 pilot aircraft and you are trying to fly it single handed and with a limited field of view with no physical feedback....a tough ask. Choose when and where to hand fly.
It is a steep learning curve for sure but if you take your time it will be an enjoyable one. The skills you learn on the 737NG can be carried across to virtually any glass cockpit Boeing machine.
If you think the 737 is hard then don't go anywhere near an Airbus