I've done the Icefields a half-dozen times, so obviously, I enjoy it. It's also the only paved north-south route thru the Canadian Rockies. That said, I've had cold (5C) and rain the last week of July - which is, technically, the warmest week of the year. I've also had lovely weather, but I'd guess my average is about 50/50.
Pluses -
Scenery - superb.
Shoulders - adequate throughout.
Services - food, camping, hostels well spaced.
Wildlife - lots to see, esp if you wander off road.
Minuses -
Expensive - daily park fees, camping - no H/B, food.
(The grocery at Lake Louise is a ripoff as is the Icefields Centre.)
Road surface - butt thumpers every 20 feet.
Traffic - can be pretty thick, esp. on a weekend.
If you do this over a two week period -
You should definitely consider adding Kananaskis.
Fabulous scenery and, in the southern section, 1/10 the crowds.
http://tpr.alberta.ca/parks/kananaskis/flashindex.asp