No, it didn't start going notably downhill until year 7. Ditching Jonas when Daniel returned was the turning point, I think. Up until then SG1 felt more epic every season; with that move, they demonstrated that the formula and maintained status quo was more important than the natural flow of the storyline, and that mindset seems to have become entrenched in the writers' thinking in the years' since then.
All the neat little bits of tech in the early years found it way into regular usage: Naquada generators, Intars, Rings, Asgard beams, etc. Back then when they found something new it actually meant something, because you knew they could pull it out to solve a future problem in a nifty way. Now they're just finding things that are *way* too powerful to let the characters keep them, so the stories inevitably explain why the tech is no good by the end of the episode. It no longer feels like they're moving forward, just stumbling in circles.
The tech problem is summarized when the stunner pistols appeared on Atlantis. Those came out of nowhere. Prior to their introduction (was it in the "Weir and Sheppard possessed" episode?), we'd only seen rifle stunners. If you want to introduce a new weapon prop, at least have the decency to give it a good "discovery" episode! They did it just fine with Zats.....
