People are raising a lot of good points in here, definitely a good topic to jump in on!
I find it a little tough, though, since it's really all subjective to how well a game executed its particular mechanic, but I'll do the bandwagony thing and attack the biggest ones on my mind that umbrella everything.
Also, I almost totally agree with everything ZeronHitaro had to say in their post above, especially about Item Crafting. I think a lot of games can do it better. I like the idea of it, but it's so rarely executed properly.
All-action, all the time: With a game like Diablo, for example. It is a fun game for a little while, but you really need to take a moment to step back from it and not play it cause, really, it's x amount of hours of grinding, and that's pretty much it. There's so little story involved, really, that what's making this a RPG is mostly the stat growth aspects. I just dislike when a game relies on this mechanic, giving me nothing else to change it up with now and again, or enough of an engaging story to make it worth it. Makes me really not interested in Diablo III because, well, I've played that game.
Easy Fast-travel: Now, I'm all about fast travel depending on the circumstance, like in Oblivion or Fallout 3 and such. If I have the time to do a full day game marathon, I like to walk everywhere, take my time, see the beauty of the world. But, if I'm just playing for an hour or so before work or another commitment, I want to maximize my questing time and get from one point to another without the waste of walking time.
Now, what I dislike about the fast travel systems is it's just too easy. I feel it should be earned or have a cost or consequence now and then. Like, in the old Baldur's Gate, Icewind Dale and Fallout, random encounters could happen and disrupt your progress. Awesome. I think in Morrowind you could only fast travel via taking the Silt Striders (I could be wrong, though, as I didn't play enough of it to find other options). But it today's games, you can just go for it. Yes, I know the game accounts for in-game time as you walk the whole distance, but there's no consequence for doing so! "I need you to do this quest for me as quick as you are able. Can you?" "Yes, of course!" Then we decide we want to fast travel to x city to get something first, walking the whole way, then fast-travel walk to the site of the quest, and thankfully the object in question is still there, the horde of goblins has conveniently awaited your arrival to begin their assault, the old man hasn't died yet, etc. I don't think you should be able to fast-travel until you can find yourself a mode of transportation, be it a horse or an old beat-up future car you happen to get going again.
Tireless Heroes: Y'know, I get why this doesn't always happen, but still, it always bugged me as a kid as to why, say, Link never needed to sleep, no matter how many days and nights he spent running across the Hyrule Field fighting off skeletons and the like. How our heroes in Secret of Mana could just run for hours and not need sleep unless you wanted the benefits of insta-healing. I always liked the Baldur's Gate and Icewind Dale had the D&D mechanic of fatigue and exhaustion if you pushed your character for too many hours. In Fallout 3, you could perpetually keep walking and never need sleep unless you wanted to heal up. There's no penalty for wandering the wastes for the next 10 days if you wanted to. Like, really? I don't want super realism, but again, I'd like some accountability.
Automaps: I like having to explore things a bit, blindly, but I like to be rewarded for that in getting the map as I go along, or even finding a copy of the map somewhere, or purchasing it. I find FFXII did this right, if I recall correctly. I think that's the game I'm thinking of... Fallout 3 does this as well, when you look at your local map, and then back. Oblivion too. I just don't want it handed to me for nothing, pointing out exactly where I need to go.
Glowing Trails, Auto Waypoints, etc: Again, I see the practical, convenience-based application of this, but whatever happened to letting us figure things out. Like, I know you can turn it off in Fable II/III, but then you pretty much have no idea where to go without it. Like, whatever happened to hints? Whatever happened to gathering information? "Go to the town of Evensley, ask around for a man named Kole. Find him and he'll give you what you need." "Travel to the east a few hours, eventually the land will break into the forest and you'll see a cavern. This is the troll's cave, where your quest shall take you." As seems to be my theme above, I like discovering things for myself, earning it, not having the developers hand it to me. If I find it and choose to assign my own waypoint, awesome. Otherwise, give me some clues! Albion is not littered with GPS markers in the Industrial Age!
Save Anywhere: I like how save points did make you strategize how you went about things, but times have changed, and games geared for late teens and adults need to take into account just how busy our lives get. We need to be able to drop the game at a moments notice and gtfo most of the time. I like that in some games it stops you if there's an immediate threat, but beyond that, you can save whenever needed, which is a great addition to any game, as Der Jermesiter said.
Grand, Open Worlds: Love having a big world to explore, that's interesting and captivating. Although it was lots of rolling hills, Oblivion's world was just plain beautiful to take in. However, I still think FFXII tops it for me. A lot of people like to rag on that game, but I think they'd have to agree that the world of Ivalice they fashioned is gorgeous. Every texture, every geographical formation, all of it filled me with a sense of wonder on every new map I stepped foot onto. On a much more narrow scope, but still filled me with amazement, is the likes of Chrono Trigger and Secret of Mana. As a kid, I always loved exploring those worlds, and how pretty they seemed, how lush and colourful and different from my own world (Well, may the Future in CT wasn't so lush, but you get the idea...)
Genuine Lore: I like the idea a lot of games are taking nowadays in trying to flesh out their worlds by providing the player with a storehouse of background info. However, in some cases, it can be overwhelming, like in Oblivion or Morrowind, with all the books you can read. Hell, I I have enough books on my REAL bookshelf to go through, nevermind the dozens of paperbacks I steal from people's shelves in game. But, the codex system of Mass Effect offered a nice, concise location for it all, and it's never too too much to read, as long as you do it in bits here and there when something seems interesting to you. It's just cool to know there's more going on than just what you see.