Much as I think DAB+ is the way forward, it is a shame that old DAB radios (which still make up a significant part of DAB listening) still show the stations as available but are then silent when you select them. It's quite a bad listener experience so I can see why they've been cautious. (for comparison, if your Freeview box doesn't do DVB-T2 channels, you're not even aware they exist).
DAB+ also seems to be heavily affected by the standard of the processing, more so than DAB to my ears. The Virgin DAB+ stations sound pretty metallic to me, like an old Real Player stream that hadn't got up to speed. Some others of the same bitrate aren't so bad. The new Global D1 stations (admittedly slightly higher bitrate) sound not bad at all. (and also it's a big relief to see Global so far using DAB+ to deliver stereo, rather than just cram in more stations)
While there is an issue with older DAB radios, of which there are still a few around, I would argue they no longer take up a significant part of listening. Thankfully Europe and Australia have been using DAB+ entirely much longer than we have, so radios have been compatible for quite some time now. Certainly all the car radios and adapters I've come across are DAB+ compatible, and I know some of the older Pure radios are software upgradable to enable DAB+.
The metallic sounding audio is entirely down to the ridiculously low bitrates being used as VMPhil suggested. You'll notice the stations using 24kbps (i.e. BFBS) sound particularly bad. The standard itself with the right bitrates can sound very good as it's just AAC audio, same as used for HD TV, downloaded music and online videos. Ideally they should be no lower than 48kbps for stereo broadcasting, but 64kbps would be best. Hopefully when we reach a point where all stations are DAB+ encoded they'll increase all the bitrates rather than trying to cram in another 10 stations, as overly compressed audio is the one thing really letting DAB in this country down.
The Global stations sound a bit better as they've made the sensible decision to use a 32khz sampling rate instead of the 44.1khz rate normally used, which means they're not trying to cram as much audio data in the limited bandwidth. The downside is you lose any audio frequencies above 16khz, but most people won't really notice that. The DAB+ stations on the SDL mux sadly haven't had the same idea.