Depends.

The Thinkpad lines (T, X, P) they bought from IBM remains consistently among the best built and most durable machines you can buy.

The cheaper lines of Thinkpad (E/Edge, L) are generally pretty good, but definitely cost-reduced relative to the main Thinkpad lines.

Their own-branded (e.g. Ideapad, and Yoga) are really mixed; it ranges from very, very good to quite cheaply built. Really depends on the model, and just like any other make you need to do your research.