Aha! You were making lunch. We were wondering why you were gone, then suddenly appeared in our intel room 20 minutes later.
I think one of the big differences between this map and 2Fort is the chokepoint in the middle. In 2Fort, if there are sentries on the bridge, you can jump down in the sewer and vice versa. If you're a scout, you can also use the roof of the bridge to get into the base. With Well, the only way to the other base is across the train tracks, so if your team can keep that defended, you can protect the intel (which is a lot like Turbine, but I've yet to see one team keep another team trapped in their base).
Yeah, and because of this, I no longer think connecting the water passages is a great idea. Perhaps they could open by the train tracks though, allowing the occasional person to slip through, but fairly easy to camp.
Here is my current position on the best strategy (coming from the perspective of a career engineer):
This map is not 2Fort, and should not be camped like 2Fort. The intel room is so hard to defend that you should focus on preventing people from reaching it in the first place, not killing them once they get there.
There are a few spots inside the base you can place a sentry (still figuring them out myself), but spies will wreak havoc on them. The fun part of this map is outside, which is where most of your team is headed, so you may have to take care of spies yourself, especially if the server is not full.
Control the middle as long as you can. This is difficult without 3 engies + teleporters to bring backup. This map is great for offensive engies, pushing the frontlines back. Teleporters are very important and
should see constant use if your team is playing right and you have them placed appropriately.
All this being said, what I enjoy the most is just sticky jumping as a demoman and using the kill command in midair to see how far my ragdoll will fly, or I use "explode" to rain gibs on everyone. Great sticky jumping map, although far too easily exploited as mentioned by PhIxX.
P.S. Everyone should check out "More late night fun on CTF Well"