I have one weird question, but I need to ask somebody on this. I´d like to know, how much detailed could the models be? When the curent version of Unity (if I have good informations) is 2.6, it means, the game made in this version is from the previous generation? Like Playstation 2, Gamecube or first Xbox? Does this mean, that the models should be “very” low polygonal or when it is ver. 2.6, it means, it could have more polygons but not so much as in today videogames? I know there are things as bump-mapping or normal-mapping, which make model more realistic. But I mean the model without textures.
That depends on your hardware, not Unity. If you have bad old hardware then you can’t do much. If you have fancy new hardware then you can do a lot.
–Eric
Your “informations” is a bit off… Unity isn’t really comparable to a Playstation 2 engine… we’re just a tad beyond that generation 
As Eric said, it depends on the hardware you’re using/targeting.
Great, that souds very good. 
Thank you.
And what is the differ betwen old generation of a one game engine and new generation of the same game engine as Unity?
And can I make with this version (2.6) the “same” games, or at least similar games as those, which are today? I mean the visual part of the game.
That depends on by what you meen by todays games. I geusse that you meen something like Gears of War or God of War 3. I think the fidelity is good but not quite that good. If you have some skills you can pull off some great looking things but there is a limit to what this engine can do. Unity 3 is really gonna beef things up but I have not heard if they are adding shaders for vegitation and terrain to accept normal, ambient occlution, parallax, specular and all the other detail enhancing greatnes available today in other top notch game engines for terrain and vegitation. Objects on the other hand can have materials that rival that of todays top notch games aside from animated normal maps and dynamic spec maps although I have not looked into this. I have limited experience with the lighting in Unity but I imagine if you know what your doing you can make some top notch environments that look like they were realistcally lit. I think Unity gives you the best bang for the buck anyways.
Thank you.