The user interface. It's garbage. It was no doubt pretty cool for 1998, but for this day and age it's garbage and it will kill you if you try to use it in a cloud without many, many hours of training. I don't like DOS operating systems either. Cool in their day I guess, but time to move on.
A piece of navigation equipment shouldn't require hours and hours of dual instruction, or hours on a simulator, an expensive power supply to train yourself on the device in the plane without the engine running, or an ap on your iPad to help you navigate the thing. People have made lucrative side businesses developing training aids for this thing because people struggle with it. The interface is garbage.
Oh, I know the tricks. I have never not gotten the engine to start. It just sucks that there are "tricks" just to get it to run. In this day and age, that really isn't acceptable. My particular engine is not consistent at all. Sometimes it really balks at starting and leaves you second guessing yourself. "Did I just flood it, or does it need more??" It always needs more gas it seems.
I may very well have a weak ignition, but there's another thing to hate. ****ty 1930's tractor ignition. I can't remember any car I've ever owned since the '70s that suffered from "weak" ignition. I have to do the 500 hour inspection just to see if it's about fail and it is due now.
It is what it is. I accept it as does everyone else who loves to fly. The point of this thread I think, was to point out downsides of the typical GA plane, not everything is A-OK and as good as it can be. Coming from an engineering background, I calls 'em as I see 'em and only because I was asked.