Anyone else think that the video should have been titled "Meat the Sandvich" instead?
Well, I've gotten a chance to play all of the new maps, and I've got to say that arena mode is a lot more enjoyable than I expected it to be. I've found that very few rounds are won by control point capture; usually by the end of one round the winner is obvious and if the round is won by CP capture, it's simply because the remaining survivors from the opposing team are trying to stall the round.
However, arena playability tends to vary heavily by map. Ravine and Lumberyard are both great (as well they should be; they were designed for the gametype). Badlands also works pretty well. However, the arena versions of Well and Granary seem pretty weak to me. To me, it just feels like they had a gametype that they wanted maps for, and said "Hey guys we can save time by just modifying some of our existing maps for the new gametype." It didn't work when they did it with ctf_well, and it didn't really work here either. I'd rather that they release the update with a small number of maps than release a bunch of maps that are just mediocre.
But as for general gameflow, I like arena for a lot of reasons. I like the fact that snipers are now actually helpful team members. I like the fact that the spy is actually useful. I like the fact that the flare gun, critzcrieg, and sandvich are actually useful as weapons. The one thing that I don't like is that critical hits exist. Crit rockets can one-shot anything but a Heavy, which isn't really a big deal in regular play since they're infrequent and you usually spawn shortly after. However, in arena mode, getting insta-gibbed by an attack that should have knocked off half your HP is really, really frustrating. I've tried searching for arena servers that have crits turned off without any luck.
As for the new payload map, I've found that it's very easy for the attacking team to reach the first three checkpoints, but virtually impossible to make it past the last point. (Red can snipe easily on the last point, but blu doesn't have any really good options for sniping. Also, the sentry alcove overlooking the last point makes it practically impossible to take out a well-placed sentry with anything other than pipe bombs, grenades, or rockets.) The plethora of heavies has made playing defense on this map a lot of fun for two reasons: one, when the attacking team is moving the cart, there are a lot of large, slow-moving backs all facing in the same direction, making it easy for a knife to make short work of the push. Second, six mobile sentries covering the cart is actually a pretty defensively-sound strategy. It's like covering the cart with sentries, except that when an uber push comes in, you have a stream of mobile sentries rushing from the spawn to intercept the cart at the next choke point.