A few quick thoughts:
Turnout was good at a shade under 40%. That's in a constituency where turnout in general elections is consistently 5-10% below the national figure. There's no doubt that this is a legitimate result that reflects the mood in Rochdale at this time.
The scale of Galloway's victory is significant. I was expecting a much closer result. Therefore, Labour's repeated claim, this morning, that they would have won, had they fielded a candidate is debatable, to put it mildly.
Moreover, Labour's insistence that they would have (should have!) won is not likely to win over disaffected voters in Rochdale. A good question to ask here is why Labour always says it must "listen to voters" when it appears to be old white racists that swing the vote, but the same logic doesn't apply to black and Muslim voters.
I doubt this result signals the seismic shift that Galloway claimed last night, but I also find it hard to imagine people's anger with Labour over its complicity in genocide will evaporate quickly. Some Labour MPS might be feeling nervous today. For example, Wes Streeting's constituency, Ilford North, has a Muslim population of 27%, which is almost identical to Rochdale's. There are hundreds, if not thousands, of ex-Labour members who who would campaign for an independent candidate to get rid of Streeting. Of course, it's important to note that revulsion to Labour's response to the genocide in Gaza is not restricted to Muslims.
Galloway is an opportunistic arse who's taken up some horrible reactionary positions (on the green agenda, law and order, trans rights) but, as far as I know, his support for Palestine has been unwavering throughout his political career. Still, I wish the victor could have been a genuinely principled left-wing, pro-Palestinian candidate.
An interesting result - far more so than I expected.