I came from an original HTC Desire, too. Really loved that phone, though sure, 500MB of RAM was never going to be anywhere near enough.
The jump to the N4 is awesome .. but then I guess you are going from v1 to v4, effectively ..
As for continually checking Play: don't bother. There is a notification option which I signed up for: do that. Sure enough, about an hour before the second lot of stock came available on Play I got an e-mail from Google and I was able to be ready and waiting immediately the Sold Out notice disappeared.
Actually, I'd read that the original stock was made available 15 minutes before the time announced, so I started checking 20 mins early. The stock didn't become available for about 5 or 10 (very tense) minutes after the time announced and it then took me several attempts to get the ordering process to work.
Got there in the end, though and I have to say I'm blown away by the N4. I love the speed (didn't even realise my Desire was that slow!), 4.1.2 is really good and I'm happy with the things most reviews complain about, namely the camera (best I've had on a phone) and battery life (got 28:30 hrs with 4:22 hrs of screen time plus hours of listening to podcasts and playing games over the w/end).
There are some things I miss from Sense - the music player and I kinda liked the clock / weather widget - but there's nothing that would make me want to go back.