I’ve used the Metro in Lisbon only a few times. There are four lines, green, blue, red and yellow. The stations are modern, clean and pretty unfriendly to handicapped people. Elevators are not always available and the concept of a cascade of elevators that’s only reachable via stairs, only to be then again terminated by stairs, is disputable.
I’ve spent my time mostly walking through the city, up and down over uneven pavement, from one hilltop to the next. If you’re bound to a wheelchair though, I can’t imagine how you could possibly get around by yourself.