First of all, there's simple beefing up the Attack values on monsters (or Magic for
spellcasters). Then there's a couple more things to explore like:
- Harmfull debuffs with a set duration (only lasting a couple turns).
These could be: Weakened, Blinded, Ablaze, Cursed, Confused (nasty!), Silenced,
Bleeding, Crippled, Entangled, Winded etc.
- Enemies (maybe Wraiths?) with Vorpal/Demonic/Nether attacks which always
deal non-reducable damage, like taking away 5 HPs every time, no matter the
Defence stat. This will make the HP stat usefull at last.
- Summoning Traps spawning not 1 but say 3-5 monsters to surround the Player.
- More punishing Traps: pits, acid, explosions, debuffs. Spikes really got old with
their miserable 1-3 dmg.
- Lower the chance to discover Traps, also, make them spawn randomly like
monsters, apart from preset trap tiles tied to some room types. If they do spawn
randomly like this already, make their rate higher.
- Traps or monsters that would make the Player Character visible for all the other
monsters on a level. (Alarm Traps, Eye of the King giving some kind of Clairvoyance
buff to its allies).
- In addition to the above one, also monsters with infravision or some other way
to see thru walls, just like Clairvoyance buff.
- Increase initial monster count when new dungeon level gets created (I mean
upon entering). Also, lower exp of higher tier monsters to keep it balanced.
- Introduce a level cap at 30 (most chars that didn't farm ad nauseum, should be
lvl 28-32 from my experience).
- Add Unidentified Potions and Scrolls, like in classic Rogue(likes), but that's going
a bit too far methinks, I guess it would have been introduced since the very beginning.