Agree with everything here, this is a great episode that hums along on the strength of its writing and performances. Eccleston's Doctor has a darkness that really suits where he sits in the timeline. Getting that first explanation of the Time War retroactively explains why he's such a dick in this incarnation: he's still deeply wounded by it but close enough to the man who did it that it very much informs who he is as a person, essentially still externalising that pain.

Something else that's interesting is that I feel this episode gives the impression that it was Nine/Eccleston who in fact took part in the Time War, while leaving things open-ended enough that that could change. Jumping ahead a bit, Moffat's earliest plan for "The Day of the Doctor" was to have Eccleston return. However, given his treatment at the hands of the BBC the first time around, Eccleston was unwilling to appear and we got the War Doctor instead. I'm not sure if RTD has ever commented on what it was he envisioned.

I've noted in previous rewatch discussions that I basically arrived fresh at New Who, but this episode reminds me that I did know Daleks couldn't go up stairs. The "ELEVATE!" reveal was a major shock to the audience and canon at the time. In addition to its general invulnerability throughout the episode, this was a scene that really hammered home the Daleks as scary. For people completely new to the series like children, it doesn't really mean anything, but anybody with a passing awareness of the show gets something in that moment to show them that Daleks are still able to do the unexpected. For adult fans, I could see this at least giving them a reminder of why they were afraid of them as kids.

The final confrontation is just amazing. That this episode manages to reintroduce Daleks, convince us they're a worthy threat, show us their true face and make us feel bad for them across 45 minutes is just excellent work from top to bottom. I'm a broken record on this, but that it's done in such a low-key and probably low-budget episode and not via an episode full of explosions and CGI is a testament to what the show can do at its best.

One thing I'll say is that it might have been interesting to call the episode "Metaltron" instead of "Dalek" to keep the surprise hidden, but I imagine that would have hurt it in terms of viewership. People definitely would have been excited to see the latest take on the Doctor Who enemy in a way that they probably wouldn't have been to see "Metaltron".

Sorry to be a downer, but I was curious why Bruno Langley, who plays Adam Mitchell ("Little Lord Fauntleroy"), seemed to drop off the face of the Earth a few years ago. If you don't want to open it, you can probably guess from the spoiler heading:

At least he's not around for long!