On Traps

One-hit-and-you're-dead traps are bad. Damage == ok. Automatically dead if you set it off == not ok.

On Mini-games

Lock-picking mini-games are fun. Three levels of different difficulties is also fun. Doing the same three levels of lock-picking mini-game 100+ times gets less fun.

A couple of different little games would be nice, rather then having the same one the entire game.

On Skills and Experience

Combat and Non-combat skills should either have different knowledge/experience point pools, or the skills should have some overlap between them; especially in game where you can't respec your points.

It's often too easy to buy lots of non-combat skills for the neat things they give you, but as a result it often ends up making the combat portion of the game difficult to near impossible; resulting in having to roll a new character.

If you have a high strength/bashing skill you should be able to break open lower-level doors or chests.

If you have a high smiting you should be able to make a better balanced, or lighter class weapons that require lower strength/dexterity to use, as well as being able to make better damaged weapons of the same type (pick one or the other when you make them, or something).

On Common Sense and Thematic Efficiency

It should not take longer to pick an item off the ground, then it takes to loot a dead body. Really.

The lean-over-and-pickup animation is cool the first few times, but after a while gets really quite tedious. If it's necessary, and option to turn it off would be useful, or just don't include it in the first place.

On Map Notes

If you use the Sorting Algorithm of Evil to place your monsters, yet have a few bigger, badder monsters around the place so people can have a challenge, it's a good idea to allow the player to make notes on the map so they can remember where the monster was so they can come back and beat it up later when they're more powerful.

The same thing happens with locked doors and treasure chests where you have neither the key, nor an appropriately high level of lockpicking skill.

On Secret Passages

Secret passages behind waterfalls always feel neat to find.

On Disappearing Stuff

Unless you've got kleptomaniac gnomes running around, having corpses and items disappear a few minutes after you've turned your back is immensely frustrating.

Sometimes you're having great fun running from combat to combat and want to come back to pick up items later. But of course by the time you've gotten bored smiting things, they've disappeared.

At the very least wait until after a "game day" or an appropriately long length of time before garbage collecting if you're worried about savegame size.