First of all, the score command will show you a bit of information about your player. An example is:

You have 500 (500) hit points, 50 (50) guild points, 0 (720) quest points and 50 (50) social points.
Your current experience is 16809 and you are level 0 in the Adventurers' Guild; your overall rating is 32.
You have died 0 times and can die 7 times before you are completely dead.
Your wimpy is set to 20%.
You are unburdened (5%) and quite comfortable.
You are neutral, worshipping no god.
You are 2 hours, 46 minutes and 6 seconds old and have logged in 17 times.

Of course, if you are mid-combat, you don't really want to have to read through all of this just to see your score.

score brief
> HP 500(500) GP: 50(50) Xp: 17055

Even more fun is the health monitor that you can make show every heartbeat during combat:

monitor on
> Your hit point monitor is set to on.

kill man
> You prepare to attack a thin man.
Hp: 500 (500) Gp: 50 (50) Xp: 17466
The thin man cuts your neck with his knife.
The thin man exclaims in Morporkian: Call the Watch!
Hp: 443 (500) Gp: 50 (50) Xp: 17472
You punch at the thin man but he parries the blow with his knife.
Hp: 445 (500) Gp: 50 (50) Xp: 17475
The thin man nicks your right arm with his knife but your skin absorbs some of the blow.
Hp: 436 (500) Gp: 50 (50) Xp: 17478
The thin man nicks your stomach with his knife but your skin absorbs some of the blow.
Hp: 417 (500) Gp: 50 (50) Xp: 17481
You punch at the thin man but he parries the blow with his knife.

You can also check other people's health, using the command:

health skye
> Skye is in good shape.