Hello again, Izzy. Kgnature is right, hamsters are nocturnal, so don't expect to see a lot of activity from him during the day, that's perfectly normal. Also, hamsters always store food in their pouches (in their cheeks) as I'm sure you know, so those massive lumps in his face are 99% of the time absolutely nothing to worry about, they're just the food he's saving for later!
A healthy hamster should be active, not lethargic, and constantly nibbling on things to keep his teeth down (if he doesn't, they may become overgrown which could cause problems with eating in the future) so ensure he has plenty inside the cage to gnaw on.
A clean, glossy coat is a good indicator that he is healthy - if there are any dull, thin or bare patches on his coat, this could indicate mites (which are perfectly curable, but it's always best to just look out for these things!) And, of course, no discharge should be coming from any of his orifices - if there is, I would take him to the vet just to be sure.
Having said all this, you don't want to be panicking every time you see his fur is wet or mucky (he could have just brushed against the water dispenser!) or if he is having a bit of a quiet day (hamsters behave a bit like humans and sometimes just have lazy days, too!) I have written a detailed hub called "Caring For Your Mouse", which also applies to hamster keepers, so have a read - it should answer any other questions you have :-) Daniella