Call me nuts, but I'm actually more fond of Garfield's older design (fatter, smaller head, on fours, ect). Nowadays, he looks more like your typical cartoon animal humanoid mascot, a standard set by the design of Snoopy, Mickey, and earlier characters.
But the artistic change that distresses me the most about Garfield is how friggin' standardized the strip looks now. Looking back at this first strip, there's a number of things that suggest an imperfect, but more organic touch to Jim Davis's art. Jon's clumps of hair, the cross-hatching on Jon's elbow, and even Garfield's proportions from the first to second panels aren't consistant. But (at least personally), I like it better that way. Although technique isn't necessarily indicative of the overall quality of a comic strip, a looser and more organic artistic style often indicates a willingness for the cartoonist to approach writing and storytelling the same way, in a more experimental and (hopefully) funnier fashion. That's why I'm always slightly saddened when a cartoonist finally hammers out a consistant style: It's sometimes indicative that the cartoon's other elements will soon become predictable and stale, and the novelty that made the strip so exciting in the first place will be gone. In all respects, Calvin and Hobbes (look at the inconsistancies Calvin's hair and Hobbes's stripes), Mutts and Cul de Sac are three comics that managed to avoid this trap, in my opinion.
Garfield's current style (I'd say from the mid-80's/early 90's onward) is guilty of blandness on an unprecedented level, to the point where it becomes a major liability for the strip. For instance, not only are all the characters perfectly proportional in all panels, but the lines that compose those characters are exactly the same thickness from panel to panel. This makes Garfield feel suffocatingly clinical and uninspiring, exactly the opposite of what good comic strip art should aim to achieve. I almost think that if Davis still personally drew Garfield himself (instead of delegating that task to an assistant), he'd be more aware of the effects of the strip's art. Then again, he was always more concerned with merchandising than art, and good art cannot cure insipid and uninspired writing, another fairly recent shortcoming of Garfield, so perhaps that wouldn't have made any difference.
And I would like to emphasize that this is just the opinion of one guy with clearly too much time on his hands.