I agree. The Impossible Astronaut and Day of the Moon are incredible. Despite being the first shard of a story that crashes on for the following year or so, it still somehow feels very whole and self-contained. The arc stuff is brilliant, with the regeneration and the astronaut and the Doctor's death - those scenes still chill my spine now - but you get the sense it could still be incredible without any of that. Because there's an absolute corker of a story at its heart, this devilishly smart whirligig of genuinely terrifying monsters across umpteen different locations, and although Day of the Moon stomps along without pausing for breath it never rushes so fast as to outpace the story - it's pitch-perfect. A properly spellbinding slab of Doctor Who.
Coincidentally, I just rewatched The Curse of the Black Spot, a couple of hours ago, which is the next episode on from Day of the Moon. For the first time, I found myself a little impatient with it. It's actually the first few scenes that set the tone - the Doctor's humour feels contrived, a little misjudged. It's the Doctor the Dream Lord hates for all his tawdry quirks. I don't think it's a problem with Matt Smith's performance, I think he performs those lines as well as possible, but I found my attention wavering. Which is a shame! Still, some nice stuff.