If you want Park's best, see his Pirates movie, with Hugh Grant. I know Wallace and Gromitt is what put Park on the map, and W&G are treasured (for good reason), but The Pirates was absolutely brilliant: a laugh a minute, inspired adventure. The process of making a stop-motion movie must be laborious, so it's a shame we see so little from Park's studios. Even though Early Man won't blow you away, it's still worth your time.
Not Park's best work? Yeah. The setup and writing is kind of slow and stodgy compared to Park's previous work, but but it's still very, very, very good content: especially when you compare it to the numerous, mind-numbing 3D animated movies Hollywood pumps out. Off the top of my head, Early Man beats out The Nut Job, Over the Hedge, Turbo, The Boss Baby, The Emoji Movie, My Little Pony... Cars... good lord, I'm making myself sick. Listing all of these subpar movies one after another like this is like eating a bunch of empty calories. Nick Park's work easily stands heads and shoulders over this mass produced crap, even if it's not his best. Early Man is *fun.* It doesn't pander to children: it's clever, fun, and the stop-motion is nothing less than charming.
A year or so ago I saw an animated DC movie, "Batman and Harley Quinn," which was truly terrible. I watch animated shows and find that I don't enjoy them. "What's wrong with me," I think. "Can all animation I see be so terrible? Am I becoming jaded?" But, hey: no, it's not me: most of the animation presented to us *is* bad. You have to see excellent content like Early Man to draw a distinction.