Well, I was a huuuge fan of Explorers of Sky, and Gates to Infinity really really disappointed me.
I'd like to see something with similar graphics to Gates to Infinity (they were very nice) but, with as much content as, if not more than, Explorers of Sky. Because that really was a monster of a game, and set up huge expectations for future Mystery Dungeon games, which Gates to Infinity definitely just did not live up to.
First and foremost, I hated that you could only start with Pikachu, Axew, and the Unova starters. And those were your only partner options as well. Not only that, but there were very few Pokemon you could befriend and all that. Not even all the Unova pokemon were in the game. I do love Pikachu and Axew, and while the Unova starters aren't terrible, they also aren't the best choices to me. In the next game I would LOVE if you could again be every single starter, including some others like Pikachu, Axew, and the old ones like Eevee, Meowth, Vulpix, Riolu, Phanpy, etc. Maybe some Kalos Pokemon could include Litleo, Pancham, maybe Goomy...? haha. Regardless I'd just like a lot more options than Gates to Infinity had.
I'm kind of mixed on the personality test. They are definitely a lot of fun, but most people are just after the specific Pokemon they want anyway, so they'll manipulate their answers to get that Pokemon, which overall makes the personality test a waste of time. I'd be fine either way.
Anyway, the lack of Pokemon also contributed to how boring it was. In Explorers of Sky, I spent hours upon hours trying to recruit all the Pokemon. It made for a really fun mini side quest thing. And getting the legendaries was actually very difficult; in Gates to Infinity, Virizion and Keldeo just join your team automatically. It's just overly boring.
Secondly, the game was pretty darn short. I finished it very fast and there was hardly anything to do after the main story was beat, which is the complete opposite of Explorers of Sky, where it felt like beating the storyline was just the beginning of the game. It just got very boring very fast...
There's other nitpicky stuff, like I hated the DLC (why can't I work to unlock things rather than pay?), I didn't relate to these characters nearly as well, and other stuff I don't care to think of right now.
There are, however, very few features I might like in Gates to Infinity that weren't in Explorers of Sky. I'm conflicted about them though, since they make the game 100x easier and kind of, once again, add to the boringness: No hunger, TMs being used over and over again, and teammates get exp points even when not brought in the dungeon.
But since this isn't an Explorers of Sky vs Gates to Infinity thread, I won't go into it.
TLDR: Here's some things from the older games I'd still like implemented.
-Have more Pokemon to choose from as your starter and partner: ALL the starters as well as a few others like Eevee, Pikachu, etc. and possibly Kalos pokemon like Litleo, Pancham, Goomy, etc.
-Keep away the personality test. (I wouldn't care too much either way, it adds a more personal touch, but ultimately it seems people manipulate it to get what they want anyway)
-Include every Pokemon (or at the very least, all but a few) to be able to be recruited, just like in Explorers of Sky days. It was fun recruiting them.
-STOP WITH THE DLC! This is probably very unlikely, since it's easy to do now with the 3DS and they're just wanting money and whatever etc etc, but I'd much rather work for more things to do than pay for it. (not just because I'm broke, but Pokemon has always been DLC-free and I've always loved the accomplished feeling of getting things after hours of trying, instead of just, here's my money. thanks.)
-Keep the 3D models. I really like them; even though the pixelly-ness really contributed to the feel of old Mystery Dungeon games, I love how beautiful Gates to Infinity was. It and the music were stunning. (Don't really need to worry about music though, as every Mystery Dungeon has consistently had striking music)
-Longer, more intricate storyline, and more to do during/after the story. Gates to Infinity was seriously lacking this and I'd like to see more in the way of things to do. The little side quests in Explorers of Sky were fantastic. Also I'd like characters to be more unique and have more depth to them... might have just been me but I didn't really feel this as much in Gates to Infinity.
-Keep TMs reusable. While this did make the game quite a bit easier... I would like to keep it this way, to keep consistent. I prefer it any way because it's much more convenient. I wouldn't totally care if this wasn't kept the same, but it probably would be, considering it's this way in the newer main series games.
-Keep away hunger. Now, this is a tricky one... while I liked not having to worry about it, hunger was really a way of keeping me on my toes and making the game more engaging and difficult. That said, it also got a bit ridiculous at times, having to fill SO many slots in your bag with apples just to make it through a dungeon. So I'd say keep it away, at least for the storyline.
In the way of new things,
-Put it on the Wii U. Crazy idea, but my boyfriend and I were talking about this before. Nintendo's Wii U was a good idea in theory, but they haven't really had many games that take advantage of the dual screens (handheld-screen) thing. I think they could make a stunning Mystery Dungeon game on this system and it'd definitely help the Wii U with sales considering it's seriously not doing so great. Mystery dungeon on a console just sounds quite interesting and I'd love to see it if they could pull it off. If not handhelds are fine, I like bringing the game with me wherever I go.
...and well that's all I can think of really. I agree not too many new things should be added, since the old games just really work, and they've been diverse/large/unique/engaging enough to pull off doing roughly the same thing each time, just making something about it more fresh. All I really ask for is the diverse options in Explorers of Sky (I mean come on, they already did it) to be put into a game with graphics on the level of Gates to Infinity (or better, of course). If they can think of some other amazing things, awesome, I'd love to see them... but, I'm not very good at coming up with game ideas myself! I'm more into experiencing them and taking them as they are. (Gates to Infinity was just hard to accept because it was pretty much a complete, obvious downgrade of Explorers of Sky)
(sorry about the wall of text! I just love mystery dungeon so much and I just hope and pray that the next Mystery Dungeon won't disappoint me so hard like Gates to Infinity did...)