Actually, while the block is the same, but the heads are re-designed by Jaguar, although I don't see why they bothered, the 3.0 produced almost identicle figures to the 220 in both power and torque. You won't find the AWD system in a Mondeo either.
From what I remember they share the basic chassis, some suspension components and the windscreen. I'm sure there are a couple of other pieces, but not much. The X-Type is built upon the basic Mondeo chassis, it is not a mondeo with new body panels.
Anyhow, the X Type is a decent enough car, if a little bland. The handling is fine, the power is fine, the comfort is fine, the styling is fine, and so on. The Sat Nav system with the touch screen makes the center console much nicer otherwise it is, like the rest of the car, fine.
The engine is thirsty mind, and may cost a bit in fuel. Jaguars figures for the 3.0, for example, are somewhat off the mark when you drive with any spirit.
If you are asking "what makes you such an expert" I had a dark grey 3.0 Sport for 8 months. I was always a bit unimpressed with the performance and was looking into supercharging it until the fuel prices got stupid and I flogged it after averaging 17.7mpg. I drove it non stop from Lille to Ashby (on the shuttle, so still sitting in the car) without stopping for a break, so I guess it can be described, for me at least, to be fairly comfortable. It never let me down, the only thing that broke was the windscreen wash bottle, which Jaguar replaced for free. Mind you, it was much cheaper to service than my Saab, which always seemed to need something doing to it, even from the independants.
If you like a sofa on wheels, with half decent perfomance, the X-Type might be for you, but something tells me that, while you'd never dislike it, you'd soon become bored with it.