Tobold talked recently about how he thinks DnD Next is the most unbalanced edition of DnD yet. Of course he calls in 5th edition and the designers just call it DnD, so I don't even know what we should be calling it. I will just stick to Next and eventually that will sound ridiculous but hopefully people will have sorted out a widely accepted nomenclature by then. At any rate Tobold thinks Next is super unbalanced because casters still get to be incredibly overpowered at high levels but they get nice things at low levels too whereas in the old editions casters were useless at low levels as a method of 'balance'. Balancing classes by making it such that for the first year of play one class is good and for the second year of play the other class is good is terrible though I suppose it is a slight improvement over one class just being superior all the time.
However, Tobold's assertions about the way Next works are completely wrong. He talks about wizards getting a cantrip they can cast at will that does 1d10 damage as if this is a big thing. Archer fighters get a cantrip that does 1d8+4 damage and has a much higher chance to hit - it is called 'shoot my bow'. Those same fighters also have the option of dropping their bow and chopping up the enemies with swords if they are so inclined and then they get to do a lot more damage. They also get way more HP, better Armour Class, and amazing passive healing. At low levels wizards are weak and flimsy in combat but do have a couple spells that will occasionally be useful - this is not different from older editions but the difference between the two classes is not nearly as pronounced in Next.
At higher levels fighters continue to do the most damage. Even on the rounds that the wizard casts one of their best single target spells like Disintegrate it is extremely likely the fighter does more damage and the fighter can do that all day while the wizard runs out of gas quickly. The only combat situation where the wizard is really unfair is AOE - there is no question that they dominate the field when there are a ton of dorks to destroy. In terms of straight up combat damage math there is no question that fighters deliver more damage than anybody against a small number of targets and that holds true from level 1 to 20.
The thing that causes problems is when combat ends and the wizard teleports the group across the world, knocks down a castle wall, goes ethereal, flies around, and becomes invisible. The fighter watches all this and sighs "So, I can jump pretty far. Anything that needs jumping over? No? Cool..." To be honest if the group is playing Next the way it is explicitly intended the wizard is probably fairly weak in combat because there are many fights in each day and they need to use many of their best spells out of combat. Also they have to know ahead of time which spells they might want to use and that will reduce their efficacy way below theoretical maximums.
So while I don't want to play Next and I think they could have done much better I do think it is better balanced by far than first, second, or third edition. Fighters are the best at fighting. Everyone else is decent at fighting and has other tricks going on that make them useful. Spellcasters are dominant at high level but not *nearly* so dominant as they were in the past. Let's give credit where credit is due - if you want old school DnD feel and you want as balanced a game as possible Next is definitely the game for you.