I have had experience up through fifth currently.
Biggest problem so far is that focus is effectively a once per battle deal. Spending a full round to try to get focus back to use again is very hindersome (the dm did not approve of my suggested houserule). Plus, the fifth level feat was much better spent on something other than psychic meditation, 6th level it will have to be for that
Changing energy missile in the way you propose does not solve the actual problem. (I will try not to talk about the save progression being fine for a specialized, small area power. I and others have run the numbers in various threads already). The important thing is to make it unable to target attended objects. Without that then a player can pretty much crippler a number of classes very easily. At least if one is forced to use a ray attack to do so then the ray might miss and it only hits one object at a time.
For the most part there are a great deal of interesting powers that are unique enough to give a good feel that is different from the other casters. Being open to slightly modifying or helping to come up with signiture powers always helps though (I have been thinking about how to make a few dozen different 'summoning' type powers to cover just about everything, given appropriate costs of course. Need a weapon? manifest one up. Need a torch? there it is. Need random piece of equipment X? go for it. etc)
For the most part the new psionics seems to be one of the most balanced forms of magic yet. There are still issues here and there (durations especially) but then every magic system has a few issues. ::shrugs::
Also, problems with various things will shift a great deal from campaign to campaign, what sort of world are you planning? Do you have any houserules? Each of those could effect various parts greatly. (I get the impression that you mean you are playing as a player, but then all of the questions still fit when modified slightly

any houserules? what is the campaign like? How open is the dm to helping come up with modified spells/powers?)
Edit: just to be clear on something though, there really isnt much in the way of 'must have powers'. For any particular build there will be, but overall not really.
I have seen some say vigor, but while it is nice (very nice indeed) it isnt necissary. My psion does not have it nor any plans to get it. Too many other powers are needed for my particular concept.
Others have said that inertial armor is required. But, psions can wear several armors with little to no penalty (rays are the big one, must get an armor with no armor check penalty) and not have to worry about it too much. Saving both the pp and the power slot for other things (also, it is much harder to dispel real armor).
I like overchannel a great deal, but a good portion of builds can find a better use for the feats. I simply like it because the character I am useing is built around useing it all of the time.. crazy guy
Psicrystal is very nice, but find out how your dm is going to rule it ahead of time. Some of the rules are a bit wishywashy, which is most unfortunate. However, between it having a few nice built in abilities, giving you alterness, and giving skill focus in something (or a save boost) it is pretty nice for just about anyone to have. Along with it being able to hold another focus (did I mention how rough focus is to use?).