A couple days late, but I guess I'll pile on the Denver transit hate
I've only visited Denver once, but using transit there, the glaring problem was that the rail services poorly connected the inner city together, they were primarily used as suburban commuting lines.
South Line: I didn't ride this one, but it seems to hug a highway and operate in lower density indistrial and SFH neighborhoods. It also serves Englewood and Littleton, which appear to be of the inner suburban variety with gridded streets and the like.
Southeast Line: This one also operates along a highway, but serves the "Denver Tech Center", an extremely car-orientated edge city, not unlike Normandale Lake or Tyson's Corner or the ones north of Atlanta. It also serves University of Denver which appeared to be a popular stop.
225 Line: Currently a pretty much useless line, an extension through Aurora and up to the East Line is underway. That being said, the line will not serve the big medical complex on Colfax, and will instead operate around it. I'm not too sure how popular a suburb-to-suburb LRT line will be, but there aren't many paradigms in the US.
West Line: Operates a few blocks south of Colfax, probably a 5-10 min walk from all the main intersections. Ridership is probably impacted by the fact that the line only operates on the Union Station branch in downtown, which isn't too close to all the big office towers.
Downing St Line: Denver's first line, not sure how well used it is. Apparently, a planning process is going on to convert the line to a low-floor streetcar (as opposed to the high-floor LRT) service and disconnect it from the lines south of downtown.
East Line: Will operate to the Airport, and replace some of the express buses that serve park and rides on the way. Otherwise, it seems to operate in industrial areas and won't attract too much walk up ridership. It does kinda serve Denver's premier new urbanist community, Stapleton.
North Line: Nothing special about this one, it seems to just serve the sprawl.
Gold Line: Perhaps a better name than the WNW Line, it doesn't serve too much except the suburb of Arvada.
Northwest Line: The proposed line to Boulder, only a short stub will be built anytime soon.
US 36 BRT: The Boulder Line in the meantime, will open soon. It's a highway BRT, with express buses using median toll lanes, and station-to-station buses using bus shoulders and slip ramps, with pedestrian bridges connecting the two sides of the highway.
Northeast Line: A long ways to go planning-wise, probably the least promising of any transit service in Denver.
One of the main problems is that the lines poorly interact in the core itself. The East, North, Gold, and Northwest lines are all EMU services that terminate at Union Station forcing a transfer to a bus to access the main office areas. The South and Southeast lines do provide direct service to downtown, but they fail to connect to the Union Station lines. The West line and branches of the SE and S lines also serve Union Station, but they run into the same problem, not serving the main part of the core.
The other issue is that Denver has completely ignored the inner city neighborhoods in favor of fast, cheap rail connections to the suburbs. The main streets of Colfax, Broadway, Federal, Colorado, etc are seeing marginal, if any improvements. E Colfax might get a BRT service, with a peak-only bus lane. Cherry Creek, which is kinda like the "Uptown" of Denver (someone correct me if I'm wrong) isn't planned to see any improvements.
As for the rail situation, a lot of it is already moving quite fast, and there isn't really any good way to change the lines to service the inner city. Hopefully a downtown LRT loop connecting the Union Station branch to the Stout/California branch (perhaps along 19th?) could improve the operation of the LRT lines and provide a better connection for the commuter rail lines.
In any case, it seems to me that the Twin Cities are doing a much better job than Denver, despite having fewer rail lines. Hiawatha and Central are high performers, Rush Line and Riverview will be pretty decent as well, Southwest, Bottineau, and Gateway are more Denver-esque, but will probably perform decently as well. We also have a much better bus system than Denver, and our SIP and Arterial BRT plans are much more aggressive at bus expansion than Denver's plans.