The thing with most dramas is that you watch relationships develop over a period of months and years. Here, you watch the relationships "develop" over a period of 17 hours, which really isn't a long period for changes to happen: they have to establish the base relationship, establish the reasons for the change, work through some of the ramifications, and bring it to a (semi)satisfactory conclusion. If they do that with staff too much, you get melodrama. If you do that with patients too much, it becomes shallow and repetitive: here's a person, you should care about them, they have this problem, you should care about that, here's a resolution and now you'll never see them again.

My understanding for series 2 is that some of the original cast is leaving and some new people coming in (and it'll take place a year later, with everyone moving up a year in medical school). So for returning characters, there'll be a big gap in their lives and they'll have to reference "events" that occurred in that gap, but they can't do too much talking about it. For new characters, they have to do the whole character introduction/care about me, balancing that with both the returning characters and the patients.

Also, in their drive to have have emotional impact, they have a very high body count: when I did my re-watch, I counted 17 deaths, an average of one per hour during that shift.

I enjoyed the show, and I fully intend to watch series 2; I just didn't find it as re-watchable as you did, and I suspect it won't do well in syndication. (How well did 24 do in syndication, anyway?)