What's the magic "thing" that's missing? I was thinking about this after I watched the episode but before I read this thread and as others have mentioned there was something... not quite there. I sort of think it's a combination of a few different things
The best races give the boys something to argue about, something to take the piss out of each other about. The "best driving roads" episodes or the Supercars in France episode were brilliant because as well as visiting cool places and getting up to the usual "hijinks" there was a constant tensions about who'd made the "right" or "wrong" choice. That ultimately at the end of the segment, one person would be right, or rather one of them would proclaim themselves right but they'd still argue over it. That didn't really happen in this race, they got the cars, Jeremy and James took the piss out of Richards car for a few minutes for it being American, the other two took the piss out of Jeremy's LFA for lacking a cup holder and... well they didn't really mention the cars much for the rest of the trip.
Another problem is, I think Top Gear has a couple of different styles that work really well. "The Cheap Car Challenge", "Jeremy in a Car vs Hammond and May on public transport", "Picking three cars and then arguing over them." But I think increasingly TG tries to mix these together in ways that don't work.
So case in point, the "Cars vs Fighter Planes" should have been done in a cheap car challenge. If the cars they'd chosen had been "Bangers", something bought for $2000 on ebay, then that challenge could have been "Modify your car so that you get shot less than the others, the loser has to go in the 'backup car'" the backup car being something suitably terrible of course, or some other penalty which actually adds some tension to the competition, makes you care about the outcome. But you can't do that in cars that cost 50k+ so instead you've got the boys driving around a track, being shot at by lasers and really... there's nothing they or their car can do that will effect the outcome. So really what's the point? It's very epic to look at I'll grant you, but there's just no tension, it doesn't matter who wins or loses... why are they even doing it again?
They're just doing it because someone decided one of these trips has to have an "epic set piece" and every series has to have a "big cross country race involving 3 supercars" but in the process it's sort of swamping the presenters, they're slowly fading into the background, being swamped by a formula of "this segment has to have this, this and this in order to make this, this and this parts of the audience happy".
But still.. TG is better than anything else on TV by a long shot, it's still the only thing I make sure I see live.