I want a final, epic battle against a massive GlaDOS robot composed of thousands of those little "eyes" she has, wherein all I have is the Gravity Gun and the Portal Gun, and I have to throw things at her head with the Grav Gun through portals because she's just that damn big. However, the only ammunition available is the eyes of which she is composed, forcing you to get as close as you possibly can, with the chance of her stepping on your puny human skull, to fetch them.
All because she is the true "face" behind the combine hundreds (if not thousands) of years after the end of Portal 2.
And then, once you finally defeat her and watch her eyes fall apart, revealing the "core" which you must then destroy in an incinerator (as an homage to Portal 1), the world shifts around you, colors changing and the background swirling into some kind of acid trip. You look around, trying to find Alyx and Barney, the only two human connections you have left. You can hear their voices, but you just can't find them. Instead, however, as you turn your head, you see "him," the G-Man. The true instigator behind all your strife. The corners of his lips raise in that vile, knowing smile of his, and the credits roll.
Please note that all of this is after you shove an (expletive deleted) with (expletive deleted) over (expletive deleted) and then take your crowbar and (expletive deleted) the Advisor.
What an end that would be...too bad Valve will never live up to my expectations. But a man can dream, I suppose.