I personally think UT2004 is a much better representation of UT99 than UT2003 could ever hope to be. They tweaked the gameplay so it's a lot better. When UT2003 came out, I bought it, installed it, played it for an hour, then fired UT99 back up. That was that.
Now, I don't think UT99 can really be captured in a game again, but UT2004 is really on the right track.
As far as the thing about there being a lack of servers and a lack of people playing on servers... it's a lie. There are tons of servers and tons of people, just the server browser kinda sucks.