I am neither thrilled nor disgusted with it. How's that for wishy-washy?
It is big, heavy, and the install isn't the most fun I've ever had. But I've found that I can get a decent install in the vehicles I've put it in, the harness height is great, etc. DS will be able to use it for a long, loooong time. A major down side is the crotch strap is 3" away from DS (he is pretty slender--40.5" tall, 38 lbs) and I have to roll up a towel and put it between his legs to prop him up, otherwise he just slides right down. I'd say for bigger or older kids it's a great idea. If I knew then what I know now, I'd have just bought two of the Nautilus. It totally depends on the kid. My niece was this size at 3 and has a stockier build; it would have been perfect for her, she'd still fit in it now at nearly 7. But for my beanpole kid it's not so great.