They make nice power, but they're not really upgradeable/tuneable. They're not "hemispherical" but they are "polyspherical" heads. I don't think "Poli" had quite the same ring to it.
We have an 04 RAM with one of these beasts in it. I'm not convinced of it's reliability yet, not to say I've had any problems with the engine itself, but I don't trust Dodge. Even worse, it gets a whopping average of 13 mpg, but the wife HAD to have the truck.
Problems not engine related: What sounded like a power steering pump whine (it's loud and intrudes into the cabin) may actually be the alternator. The instructions for lowering the spare tire in the manual were completely wrong. The locking lugs from the factory were made of potted metal, and installed too tight. They broke when I ended up running over a bolt and tried to put on the spare. The centercaps the truck came with were wrong and fell off. The locking lugs faux cover fell off. The passenger door leaks like a son of a ***** and won't stay tight for anything when adjusted. The sliding rear window rattles like a *****. It's burnt two tail lights (in comparison, my Corolla is a year older with twice as many miles and has never had a lamp out). When trying to disassemble the dash, there is a screw behind the hook on the lower dash that is 100% impossible to unscrew.
Seriously, I hate that damned truck, but the wife had to have it.