It's weird that, despite being a fan since the early 80's, it wasn't until Tennant left that I felt I'd really experienced a proper regeneration.
The first I remember was Four to Five, and I was only 7 years old then so I don't remember having any real emotional investment in it. Davison was the first Doctor that I have specific memories of watching every week, and I guess that's when I first became a 'fan' of the show. But even when he left, I still don't think it was a big deal for the 11 year old me.
And then, of course, it was a while before we even had a noteworthy regeneration. Six to Seven was a pre-credit sequence, Seven to Eight happened in the first 20 mins of the movie and McCoy has all of about 5 lines prior to it happening and Eight to Nine happens off-screen.
And with Chris, we knew he was going almost immediately after he debuted. So even for his regeneration, as good as it was in the context of TPoTW, I still didn't feel like I was 'losing' a Doctor.
But with Ten, all those years and all those regenerations after Tom fell onto that grassy knoll, this one felt real. And certainly for me, all the build up to it worked. As Ten's last moments played out, it was like I suddenly realised he was going. Up until that point, I'd been all hyped about TEOT and how Ten was going to 'die' and our first glmpse at Eleven. But when Ten began his slow walk to the Tardis after saying hello/goodbye to Rose, it was like... "Oh hang on. He's really going. He's not going to be the Doctor any more."
It was like when a work friend is leaving and they're gonna have a party. You get all excited about the drinking and the dancing and inappropriate snogging. But then the evening draws to a close and it suddenly hits you that that person is leaving and you're gonna miss 'em and you get all emotional.
Don't get me wrong, I'm not saying I wish DT hadn't left. The time was right for 10 to go (even if he didn't wanna

) But in terms of how RTD wrote 10's regeneration, it was one of the very few things that TEOT did exactly right.