I was one of the players in the Thursday 1pm slot that James Wyatt detailed in his
blog. It was great to have my first taste of the 4e rules with one of the core members of R&D. James is a fun DM and was excited to share as much of the mechanics of the game as he could.
The dragon encounter was difficult indeed. We had a smart table who learned quickly to work together well, but none of us could make our saves against the ongoing breath, and we also failed Perception checks so the dragon got its surprise round (Darkness, breath). Even worse, it won initiative so it got another suite of actions before the first PC could act in Round 1 Actual. It blocked us from actually getting into the room and most of the battle took place in the corridor, which made us cry.

However, them's the breaks of initiative. You pays yer money, you takes yer chances.
Despite our poor start, we almost bloodied the thing (I think we reduced it to 167/280). I played Corrin, the halfling paladin, and I would've been the 4th casualty had I not rolled two straight 20's on death saves. The encounter was challenging and entertaining, and I didn't think it was unfair, just extremely difficult. We didn't encounter any black-flame braziers or such... just the horrible acidic fury that was the dragon. Despite having three deaths, we felt that we gave it our best effort. The dice were unkind in that encounter, especially the "clinging" ongoing 5 acid damage each round. The stun and the dragon's APs was just insult to injury. But I wouldn't trade the experience for anything... it was a suitably epic battle for 1st-level PCs. Keep in mind it was a Level 4 Solo monster: a suitable challenge for a party of five 4th-level characters. It was there to kill the disposable pregens and show off the system's capabilities for monsters (James said as much).
Someone up in this thread said the 3.5 LG Special was harder. We played that one at APL6 and I agree that it
was harder, but our superior system knowledge of 3.5 prevented any deaths (we finished the special; achieved all objectives).
Thanks to playing with Mr. Wyatt and piggybacking on his 4e system knowledge and willingness to teach, I felt much more confident in the LFR preview 1 (Sembia), which we breezed through in comparison to Scalegloom. My experiences with 4e in the two previews, as well as the Delve, convinced me that 4E is worth supporting for organized play. I'll be DM'ing LFR modules in 4E for years to come, but I will keep the flame of my beloved 3.5E alive for Gaia's Dream, Pathfinder and the DCC World of Aereth.
Nick