Brain control, images projected onto your retina, so it fills your entire field of vision and a slightly different perspective into each one for a true 3D illusion.
Better physics, such as real material simulation and fluid simulation, much better AI that can approximate the difficulty of a human opponent with apparent intuition and foresight.
graphics have a ways to go still but I don't think you will see the noticeable jumps that we did from the SNES->N64->PS2->PS3 in the past, mostly just higher poly counts (or a better technique altogether), higher res textures, more texture layers to better approximate realistic surface lighting, more light sources (most scenes even in modern games are lit by only 3 light sources, it's extremely computationally limited)... I don't know what more can be done with pixel shading, it's pretty fantastic as it is, what more can be done when you can use almost any algorithm you can think of for the script?
MMO's specifically will boom, riding the coattails of the aging WoW, which is still the undisputed champion by a wide margin. I can only hope they offer more dynamic worlds, with constant events, possibly even user created events where users could have some limited or temporary control of the game world (think building things, moving around objects to setup an environment, stuff like that). For those of you who have played WoW, imagine a guild common area, where you and your guild members could directly control the objects in the area. You could set up a trophy shelf with trophies from boss kills, you could have various rooms linked to different ventrillo channels, you could buy various useful objects, like forges and things for crafting and have them right in your own guild hall... stuff like that I always thought was missing. This wouldn't be some virtual area off of the map that you get to with a UI command or anything... it would be a physical location in the world that other people could visit, if you allow them to.
Furthermore with MMO's, I would hope the grinding quests, collect X number of these things, kill Y number of these things, will soon be gone forever. I would love to see more meaningful content, perhaps added on a daily basis, perhaps even community driven. Imagine if guilds could host a quest of their design each day/week that is acquired by visiting their aforementioned guild hall, possibly in the form of some competition with some entry fee and a prize for the winner donated by the guild bank. Some sort of quest template would be used to create the quest, but done in such a way that the number of possible combinations would be nearly limitless.
I'm rambling, but I see so much potential for MMO's in the future beyond the pointless killing and gathering quests that you see today, the difficulty is allowing the community to create content without the need for formal knowledge of programming, scripting, texture generation, or 3D modeling...
