i have both the 3/4 and full length altura extreme waterproofs. The 3/4's are an excellent compromise for showery (even heavy spells) and standing water combined with my seal-skins (only shortish ones). teamed up with lycra shorts, and splashing trhough big puddles, you can get splashing up the inside, which makes them feel a bit cold next to the skin, but this would be solved with 3/4 length lycra, which I plan on getting soonish.
For full on constant & steady rain and commuting to work in wet weather I wear the full lengths. They work very well for me – I thought they'd annoy the hell out of me like previous cheaper trousers, but they articulate very well, and the adjustments they have mean you can get them well out of the way of drivetrain.