An incompetent DM will only ever say "you hit" or "you miss", when you hit or fail to hit, respectively. This turns combat into a pure numbers game, which is fun enough for some people but boring for most people.
A half-competent DM will, instead of saying "you hit", say "you hit him in the [location semi-arbitrarily chosen on the fly based on how much you beat his AC by and how much damage you wind up doing]!" This is more interesting, but still not perfect.
The rare good DM will also tell you how you miss. It's odd that this is rarer than the above, because it's actually very easy to do. You can set up rules for it in your head! A good DM will keep a general sense of the monster's various kinds of AC, and will declare how you failed to hit based on those, based on rules like these:
- If you rolled below 10 and didn't hit, you missed.
- If you rolled above 10 but below his touch AC, your foe ducked or otherwise deliberately evaded your attack.
- If you rolled above his touch AC but below his total AC, his armor or natural armor deflected the blow.
- If your foe has a dodge bonus, then you can use the word "dodge", and your foe dodged the attack if you rolled higher than 10+dex but lower than 10+dex+dodge.
- If your foe has a deflection bonus, same deal. If your foe has a shield bonus, same deal. If your foe has any other kinds of bonuses, same deal.
In general, a foe will let an attack sail past them if it would miss on its own. If it could actually hit them, they prefer to get out of the way. If they can't do that, they'll prefer to block it with something that can reliably do so, e.g. their shield or deflection bonus. If they can't do that, only then will they take it on their armor or thick hide (i.e., natural armor). And if they can't do that, then you hit.
This makes combat much more interesting, and communicates some information that the characters really should have, and which particularly smart players (if there is such a thing) can leverage. If they notice their foe catching most of their blows on his shield, they'll know to sunder it. If they notice their foe ducking out of the way of most of their blows, they'll know to cast grease to make him flat-footed. If they notice their foe catching most of their attacks on his armor, they'll know to use more touch attacks. And so on.