As others have noted this is not the best special they've done, but importantly it *is* a special - yes, finally, at the end of the season, we get treated to one.
How much I've missed the hour-long specials that save us from the tedious and unfunny introductions to 'conversation street' and the infinitely worse celebrity segment. I always thought, throughout the first season, that although the celebrity segment wasn't in the least bit amusing, it was at least short. This season it's like they're punishing us for daring to complain about the celeb section by making it take up about a third of each episode's running time (ergh!).
So if only for that reason alone the special gets extra marks.
As for the merits of the special itself, well the concepts they came up with were of course fatuous (even for the trio's standards), but people taking offence to the special are either being entirely too delicate or are missing the point that it's meant as a (very good) parody of celebrity engagement with world poverty/hunger.
The other reason specials are so much better than the other content on GT (and TG before it) is that it allows for spontaneous comedy, rather than the canned, scripted gags that usually fall flat throughout the rest of the show. So they were plenty of moments of off-the-cuff humour that are the best parts of the trio's routine. The location and journey wasn't as good as most other specials, and the task didn't evolve as they progress, which is the episode's main weakness for me.
Still, probably the best episode of the season, if only for the fact that it's an hour-long special that spares us from the worst parts of the regular episodes.