Portland drivers are actually not too bad (as compared with places like New Jersey, where driving a car is taking your life into your own hands). They've driven in the rain so often that it's barely even a concern, but for the unwary traveller with a rental car, the experience can be harrowing. Wet conditions require some getting used to -- pay attention to your fellow drivers.
Coming into Portland from the East is usually along the 76 freeway. This is also called the "Bandfield", and I will warn you now: it is almost always congested during rush hours both a.m. and p.m.. If you do drive in this way, though, further past Gresham is the most stunning view of the Columbia Gorge that you're ever likely to find.
From the North, you'll probably want to take the 405 instead of the 5, simply for traffic reasons. The pictures below are from the car window of the city -- a view that shows why the city has the monniker "Bridgetown", given the amazing vista views across the Columbia and Willamette rivers.
If you do take the 26 out of Portland itself, there is something I've nicknamed the Magic Tunnel (see pictures below). One minute, you're in the city. You enter a tunnel, and on the other side, you are mystically transported to a northwest vista -- nothing but curves, hills, and trees.
It is advisable (as if you haven't gathered as much from the other entries), to take public transportation when going into Portland from the suburbs. It's cheap, under $2 in most cases, and free if you're within Fareless Square. The bus system is extensive and runs from early morning hours until just after midnight -- very convenient for just about any purpose.
Portland is a wonderful city. Its focus on preserving its natural beauty is evident around every turn. Stay safe while travelling by car -- pull over if you'd like to admire the views of Mt. Hood rising over the city. I've seen way too many accidents involving tourists, cameras, and a 65 mile-an-hour car.