Sabin_Stargem: Something that I liked from Illusion of Gaia was how there was no grinding for increasing your power. Instead, each room had a set of extra enemies that would give a stat boost when defeated. Once cleared, those extra enemies will not return.
I very much appreciate treasure radars and counters. Being able to know that an area has been cleared of stuff to find is a time saver.
When it comes to tile-based dungeon crawlers, I would like them to use a mapping system similar to Etrian Odyssey. You put down the walls and markers, eventually creating a useful map. It is extremely rewarding to play a Newgame+ and finding your maps preserved.
Tyrian has a slightly different money system: Trading in equipment or downgrading will return 100% of the money that you have invested. I think this is very cool, as it encourages the player to try out all kinds of gear.
Some RPGs provide the ability to infinitely avoid enemy encounters. Of course, you would miss out on the experience and drops they could have provided. Extremely useful when you don't feel like fighting through a horde of baddies.
If you liked Illusion of Gaia's lack of grinding, you will like Super Mario Bros.'s lack of grinding. In Super Mario Bros., you can't backtrack (without dying or going into a pipe that takes you backwards, and the latter is rare), so there is no way that enemies can respawn.
Ultima 3 is like Tyrian in that you can get back your full investment when you sell it.
Avoiding enemy encounters in RPGs has a few issues. First, quite often the enemies move in real time, turning the game into an action game, especially when you are trying to avoid enemies. Second, being able to avoid encounters at no cost breaks resource management challenges; a better solution would be to have encounter evasion use up a resource and have enemies drop immediate pickups that restore that resource and other resources.
(An immediate pickup is an item that has an immediate effect when picked up and can't be saved for later; an example is the small hearts in most Zelda games that restore one heart of health when picked up.)