Personally, I think it's more fun when the CP is volitile.
It's not that hard to set up a sentry, especially with all the weapon drops. Close games are always way more fun than one team dominating the other.
'Seconded. I honestly can't wait for koth_ nucleus. One of the most annoying things about that map is how sniper friendly it is. (I play with a lot of good snipers, so I can rarely leave spawn unless I'm a spy or scout) However with the King of the Hill style play this map should be a lot more fun. The "hill" will most likely change hands quite a bit, which is the enjoyable part of koth.
I've actually always felt this aspect of Watchtower was a strong point, not necessarily poor design. It's far different from how most Arena maps play, but I've always felt it had a good flow to it and I like its focus on vertical gameplay. I do obviously have to agree that it'd be great for KOTH though. I hope the guy who made Watchtower won't mind putting it out as a KOTH map..
I hope Valve doesn't feel like they have to innovate with every update either--I'd love to see some new Valve-made A/D CP maps.
Vertical gameplay does not work well with tf2. Granted, it's not a bad thing to have vertical gameplay, but when a map is solely based around that idea it limits the amount of classes that can play it. Unless I set on the point all day long, I feel completely useless as a heavy or engie on that map. Even spies have a tough time because unless your on the pipes or in the watchtower itself, the map is too open. Arena mode is meant for any class to battle with each other, and not to focus on the capture point, which is why the layout of the map is very very important.
However, KotH style is very different. Instead, the gameplay is focused on holding the control area rather then directly fighting one another. The problem with watchtower is that when it's played in arena mode the map focuses on the control point rather then person to person combat.