Even if I'm a huge fan and I regard him as my favorite rock musician, I'm the first to admit that he can be very sloppy, and that his phrasing is anything but clean and articulate, especially when it comes to lead guitar.
On the other hand, I find him a rather inventive and expressive player - the execution isn't always up to standards, but he goes to interesting places and pushes some interesting buttons. The solo in the live version of No Quarter on The Somg Remains the Same still is one of my all time favorite - and that one isn't as sloppy as some others.
I also like the way he blends styles and techniques and twist them around and adapt them to make up for his limitations. His rhythm works is remarkable - the way he layers those tracks, the tones he's uses and how he combines them, his predilection for odd/ugly tones and the way he resolves them into a bigger picture, the voicings he uses... And his acoustic work.
Funnily enough, having just recently got into Rush after a lifetime of intense dislike, one of the first things that struck me was Alex Lifeson's choice of tone - I almost felt like I was hearing a less sloppy and less radical Jimmy Page.
Watching an interview last night, I was amused to hear Lifeson mention how he used to worship Jimmy Page.