Not sure what 'good' is supposed to mean!

Armature; - Try operating the drill and twisting the chuck by hand (in the correct direction). If it starts then: Commutator ring: Is it shiny? If not take it out and clean carefully with some plumber's grade of wire wool. Make sure you clean it carefully afterwards to get rid of all the wire wool bits.

If that fails, What voltage do you get at the brushes when the trigger is pulled max?

Check the condition of the battery contacts in the base of the drill. They get worn/pitted/carbonised with use and whilst the poor connection is able to supply enough power to light the work LED (very, very little) as soon as you ask for enough juice to turn the motor, the resistance is too great and nothing happens. It is very similar to the effect in a car when the accessories, dash lights etc work but the engine won’t turn over - due to a poor battery connection. A new contact assembly is very cheap and easy to change (UK£10 or so).