Throwing terms like "5th Generation" around with a first flight by a prototype is reckless. What can we tell from the video about the aircraft? Very little other than it was a fairly typical first sortie of a developmental system. The planform looks remarkably like an F-22, so it would be reasonable to credit it with a fairly low RCS (radar cross-section) but we should note that the prototype F-22 first flight took place in 1990 and there has been a long and tortuous road to the current capability of the aircraft which the T-50 is clearly intended to challenge.
Remarkable Event Says Putin
A gear-down flight of a new airplane can certainly be characterized as "remarkable" but it doesn't really say much about capability as a weapon system.
Russian Deputy Prime Minister Sergei Ivanov told the cabinet more work had to be done on the engine and the armaments system.
What that means is that the prototype is flying with temporary engines taken from the Su-30, not a supercruise capable, low IR signature engine suitable for a stealthy 5th-Gen fighter. The installation on this prototype look distinctly unstealthy both from radar and IR perspectives. If fully vectorable as in the Su-30, they would also flash huge returns to opponent sensors as they move.
It also means that the true core of capability of a state-of-the-art stealthy air-dominance platform has not yet been developed. A modern weapon is more than an agile airframe. Low emission sensors, data fusion with supporting platforms, situational awareness presentations and beyond-visual-range independently targetable weapons are not yet fitted to the aircraft.
The predictions of large scale sales to client states and operational capability by 2015 lead me to believe that this is a very impressive aerodynamic platform, much like the Su-30 video we looked at last week, but which will fall far short of the operational capability of the F-22 in air superiority roles and the F-35 in ground attack.
One should never minimize a potential adversary's capabilities, but one should also be cautious about accepting completely the advertising campaigns of a marketing agency, particularly one which has a track record of high volume, low quality production.
We'll see on this one.