Decent bikes. DOHC motors so the fist really big issue is the timing chain. The DOHCs were slightly more fragile than their SOHC counterparts which means they are still anvils but there are some small things you need to watch.
First off if it has been sitting the caliper will invaribly need a rebuild. It is a fact of life any cb750 caliper will be the frist thing to freeeze up.
Timing chain life is uber important on these bikes. Unattended and the tc has been known to saw the motor in half. As long as the bike is not making any strange timing chain noises you should be good. Just make sure the tension is set right and the chain replaced at regular maintenance intervals.
The valves are bucket and shim adjust so a valve job is kind of a pain in the ass. They rarely go out but it is always recommended you pay attention to any top end noises on these motors. I think you have to do a valve adjust every 30 or 50K or something ubsurd like that.
A big issue with these bikes is the starter clutch. They tend to work loose and make all sorts of noise. If you are not careful they will tear up the flywheel. It is a 30 minute fix and will probably cost you about $40 in parts to put a new starter clutch in there and locktite the bolts.
voltage regulators can be an issue on these bikes as well as pulse controllers. As long as you have 4 fat sparks and she is charging above 2000 rpm you are good to go.
Carbs are cv carbs. Good all rounder carbs but lousy performance carbs. They gum up easily too.
they are very easy bikes to ride, the single disc leaves a little to be desired so if you have a comstar model, upgrade to the F dual disc setup. The bike can be a little heavy but you'd never know the way it handles.
As far reliability, there is a huge black guy in the city here that has about 80K on his. Rides it everyday everywhere. I have seen him ride in snowstorms I would not drive in. He has a lot of faith in these bikes. I do to.
the motor is the same as the F and the C. if you get tired of the 750 mill you can always try and find a 900F mill and drop her in.